Questions: Metals and Non Metals

Concepts of Metals  and Non Metals

In text Questions page number 40

Question 1. Give an example of a metal which (i) is a liquid at room temperature. (ii) can be easily cut with a knife. (iii) is the best conductor of heat. (iv) is a poor conductor of heat.

Question 2. Explain the meanings of malleable and ductile.

In text Questions page number 46

Question 1. Why is sodium kept immersed in kerosene oil?

Question 2. Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water

Question 3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.

Question 4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute sulphuric acid.

Question 5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

In text Questions page number 49

Question 1.(i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of Na2O and MgO by the transfer of electrons. (iii) What are the ions present in these compounds?

Question 2. Why do ionic compounds have high melting points?

In text Questions page number 53

Question 1. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue

Question 2. Name two metals which are found in nature in the free state.

Question 3. What chemical process is used for obtaining a metal from its oxide?

In text Questions page number 55

Quesiton 1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

Question 2. Which metals do not corrode easily?

Question 3. What are alloys?

Text Book Exercise

Question 1. Which of the following pairs will give displacement reactions? (a) NaCl solution and copper metal (b) MgCl2 solution and aluminium metal (c) FeSO4 solution and silver metal (d) AgNO3 solution and copper metal.

Question 2. Which of the following methods is suitable for preventing an iron frying pan from rusting? (a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) All of the above.

Question 3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be (a) calcium (b) carbon (c) silicon (d) iron.

Question 4. Food cans are coated with tin and not with zinc because (a) zinc is costlier than tin. (b) zinc has a higher melting point than tin. (c) zinc is more reactive than tin. (d) zinc is less reactive than tin.

Question 5. You are given a hammer, a battery, a bulb, wires and a switch (a) How could you use them to distinguish between samples of metals and Non-metals? (b) Assess the usefulness of these tests in distinguishing between metals and non-metals.

Question 6. What are amphoteric oxides? Give two examples of amphoteric oxides.

Question 7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Question 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Question 9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (a) What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper? (b) Write a balanced chemical equation for the reaction taking place.

Question 10. State two ways to prevent the rusting of iron.

Question 11. What type of oxides are formed when non-metals combine with oxygen?

Question 12. Give reasons (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Question 13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Question 14. Differentiate between metal and non-metal on the basis of their chemical properties.

Question 15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Quesiton 16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron)

Make a comparison and write down ways in which plant cells are different from animal cells.

1. Make a comparison and write down ways in which plant cells are different from animal cells.
Answer:

Plant Cell	Animal Cell
1. They are larger in size.	1. They are smaller in size.
2. Cell wall is present.	2. Cell wall is absent.
3. Lysosomes are absent or very few in number	3. Lysosomes are larger in number.
4. Plastids are present.	4. Plastids are absent.
5. Subunits of Golgi bodies known as dictyosomes are present.	5. Prominent Golgi bodies are present.
6. Vacuoles are larger in size.	6. Vacuoles are smaller in size.

Why are lysosomes known as suicide bags?

3. Why are lysosomes known as suicide bags?
Answer: Lysosomes are called suicide bags because in case of disturbance of their cellular metabolism they digest their own cell by releasing own enzymes.

Where are proteins synthesised inside the cell?

4. Where are proteins synthesised inside the cell?
Answer: Ribosomes are the site of protein synthesis inside a cell. They are either free or attached to Rough Endoplasmic Reticulum(RER).

If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer: The damaged cell will not able to perform vital functions like respiration nutrition, removing wastes and making proteins.

Can you name the two organelles? we have studied that contain their own genetic material?

1. Can you name the two organelles? we have studied that contain their own genetic material?
Answer: The cell organelles plastids and mitochondria have their own genetic material.

differences between prokaryotic and eukaryotic cells.

1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Prokaryotic cell	Eukaryotic cell
1. Size : generally small ( 1-10 µm)    Where 1 µm = 10-6m	1. Size: generally large ( 5-100 µm)
2. Nuclear region: It is not well defined and known as nucleoid.	2. Nuclear region: well defined  and surrounded by a nuclear membrane
3. Chromosome: single	3. More than one chromosome
4. Membrane-bound cell organelles absent	4. Membrane-bound cell organelles are present.

Why is the plasma membrane called a selectively permeable membrane?

2. Why is the plasma membrane called a selectively permeable membrane?

Answer: The membrane is called selectively permeable membrane because it allows selective materials like gases water and wastes not all to move in and out of a cell.

How do substances like CO2 and water move in and out of the cell?

1. How do substances like CO₂ and water move in and out of the cell? Discuss.
Answer: Gases like carbon dioxide and oxygen move in and out of a cell by diffusion from the region of high concentration to low concentration.

Why is the cell called the structural and functional unit of life?

2. Why is the cell called the structural and functional unit of life?
Answer: Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells.

Who discovered cells, and how?

1. Who discovered cells, and how?
Answer: Robert Hooke discovered the cells. He saw that the cork resembled the structure of a honeycomb consisting of many little compartments. Cork is a substance which comes from the bark of a tree. This was in the year 1665 when Hooke made this chance observation through a self-designed microscope. Robert Hooke called these boxes cells. In this way he discovered the cells.

Which of the following are chemical changes?

Question 11. Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle.
Answer: Examples of chemical changes are
Growth of plant, Rusting of Iron, Cooking of food, Digestion of food, and burning of candle.

Classify the following into elements, compounds and mixtures.

Question 10. Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood
Answer: Classification of the given substances in elements compounds and mixtures
Elements:     Sodium, Silver, Tin and Silicon.
Compounds: Calcium carbonate, Methane and carbon dioxide.
Mixtures:      Soil, Sugar, Coal, Air, Soap and Blood.

Which of the following will show “Tyndall effect”? (a) Salt solution

Question 9. Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution.
Answer: Tyndall effect is shown by colloidal solution. Here milk and starch solution are colloids therefore milk and starch solution will show Tyndall effect.

Identify the solutions among the following mixtures. (a) Soil (b) Sea water

Question 8. Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water.
Answer: Out of the above mixtures Sea water, Air and Soda water are solution.

Which of the following materials fall in the category of a “pure substance”?

Question 7. Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air.
Answer: Out of the above substances only Ice, Iron, Hydrochloric acid, Calcium oxide and Mercury are pure substance.

How would you confirm that a colourless liquid given to you is pure water?

Question 6. How would you confirm that a colourless liquid given to you is pure water?
Answer: Take a sample of colourless liquid and put on stove if it starts boiling exactly at 100 ºC then it is pure water. Any other colourless liquid such as vinegar always have different boiling point. Also observe carefully that after some time whole liquid will convert into vapour without leaving any residue.

xplain the following giving examples. (a) saturated solution (b) pure substance (c) colloid

Question 4. Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension
Answer:

(a) Saturated solution: Solution in which no more solute can be dissolved at a particular temperature is known as saturated solution. For example in aqueous solution of sugar no more sugar can be dissolved at room temperature.
(b) Pure Substance: Any substance is said to be pure if and only if it is made up of single type of particles means all the particles of that substance should be of same chemical nature. For example water, sugar, salt etc.
(c) Colloid: A colloid is a heterogeneous mixture whose particles are not as small as solution but they are so small that cannot be seen by naked eye. When a beam of light is passed through a colloid then the path of the light becomes visible. For example milk, smoke etc.
(d) Suspension: A suspension is a heterogeneous mixture in which solids are dispersed in liquids. The solute particles in suspension do not dissolve but remain suspended throughout the medium. For example Paints, Muddy water chalk water mixtures etc.

Classify each of the following as a homogeneous or heterogeneous mixture.

Question 5. Classify each of the following as a homogeneous or heterogeneous mixture.
Soda water, wood, air, soil, vinegar, filtered tea.
Answer:

Homogeneous mixtures: Soda water, air, vinegar and filtered tea.
Heterogeneous mixtures: wood and soil.

Pragya tested the solubility of three different substances at different temperatures and collected the data as given below

Question 3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
Answer:

(a) At 313K 62g of potassium nitrate dissolved in 100g of water. So to produce a saturated solution of potassium nitrate in 50g of water we need  of potassium nitrate.
(b)Some soluble potassium chloride will separate out in the form of crystal at room temperature because the solubility of potassium chloride will decrease.
(c)

(i)  Solubility of Potassium nitrate at 293K is 32g.
(ii)  Solubility of sodium chloride at 293K is 36g.
(iii) Solubility of Potassium chloride at 293K is 35g.
(iv) Solubility of Ammonium chloride at 293K is 37g.                                                      
The solubility of Ammonium chloride is highest at this temperature.

(d)The solubility of salt increases with the increase in temperature.

Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Question 2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer:

(i) Tea can be prepared by following steps:Take 100ml of water as solvent and boil it few minutes.
(ii) Now add one tea spoon sugar, one tea spoon tea leaves and 50ml of milk. Here sugar, tea leaves and milk are solute.
(iii) Now boil it again for few minutes so that sugar will dissolves in solution as sugar is soluble in water
(iv) Now filter the solution. Collect the filtrate in cup. The insoluble tea leaves will be left behind as residue.

Which separation techniques will you apply for the separation of the following?

Question 1. Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer: (a) Sodium chloride from its solution in water  Evaporation.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride    Sublimation.
(c) Small pieces of metal in the engine oil of a car  Filtration
(d) Different pigments from an extract of flower  Chromatography.
(e) Butter from curd  Centrifugation.
(f) Oil from water  Using separating funnel
(g) Tea leaves from tea  Filtration
(h) Iron pins from sand  Magnetic Separation
(i) Wheat grains from husk  Winnowing
(j) Fine mud particles suspended in water  Centrifugation.

Which gas is usually liberated when an acid reacts with a metal?

Question 2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Answer: When acids react with metal generally hydrogen gas is produced. We can test it by bringing burning candle near to it then it will produce pop sound.

Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds

Question 1. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer: When HCl or HNO₃ are mixed with water then they dissolve in water to form H⁺ or H₃O⁺ ions which shows their acidic character. For example just see the following reactions

When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.

You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8

Question 1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer: The pH value of a solution varies from 0 to 14. The pH value is 0 for a very strong acid and the pH value is 14 for a very strong base. The pH value is 7 for a neutral solution. Hence A is acidic and B is basic in nature. The concentration of hydrogen ion decreases from pH value of 0 to 14 therefore A has more hydrogen ion concentration.

Under what soil condition do you think a farmer would treat the soil

Question 4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer: If the soil is acidic in nature which is not suitable for agriculture then the farmer would treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).

What is the common name of the compound CaOCl2?

Question 1. What is the common name of the compound CaOCl₂?
Answer: Bleaching Powder.

Name the substance which on treatment with chlorine yields bleaching powder.

Question 2. Name the substance which on treatment with chlorine yields bleaching powder.
Answer: When calcium hydroxide is treated with chlorine gas it yields bleaching powder. It is shown in the following chemical reaction.

What will happen if a solution of sodium hydrocarbonate is heated

Question 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer: When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.

You have been provided with three test tubes. One of them contains distilled water

Question 1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer: If the colour of red litmus does not change then it is acid. If the colour of red litmus changes to blue then it is base. If there is slight change in the colour of red litmus (such as purple) then it is distilled water.

Name A, B, C, D, E and F in the following diagram showing change in its state

Question 9. Name A, B, C, D, E and F in the following diagram showing change in its state

Answer:

(i) A->Fusion
(ii) B->Vaporisation
(iii) C->Condensation
(iv) D->Solidification
(v) E->Sublimation
(vi) F->Sublimation

Now read the following concept for reference 

Interconversion of three states of matter: Any state of matter can be converted into other state with the help of temperature or pressure. Different terminology for the Interconversion of states of matter is given below:

(i) Solid to Liquid: Fusion
(ii) Liquid to Gas: Vaporisation
(iii) Gas to liquid: Condensation
(iv) Liquid to Solid: Solidification
(v) Solid to Gas: Sublimation
(vi) Gas to Solid: Sublimation

Observe the following diagram to memorise this Interconversion states of matter:

What produces more severe burns, boiling water or steam?

Question 8. What produces more severe burns, boiling water or steam?
Answer: Steam will produce more severe burns than boiling water because steam has more heat energy than water due to its latent heat of vaporisation. 

Why is ice at 273 K more effective in cooling than water at the same temperature?

Question 7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer: At 273K or 0 ºC the ice will give more cooling than water because it can absorb more heat than water due to its latent heat of fusion.

Give two reasons to justify (a) Water at room temperature is a liquid.

Question 6. Give two reasons to justify
(a) Water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Answer: (a) water at room temperature is liquid because at this temperature (i)it has fixed volume and (ii)it can flow.
(B) An iron almirah is solid at room temperature because at this temperature (i) it has definite shape along with fixed volume and (ii) It can not flow like water and hence does not possess fluidity.

What is the physical state of water at (a) 25°C (b) 0°C (c) 100°C?

Question 5. What is the physical state of water at (a) 25°C (b) 0°C (c) 100°C?
Answer: (a) Liquid, (b) Solid and (c) gas.

Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

Question 4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen. 
Answer: The force of attraction between the particles increases as we go from liquid to gas so the required order is: Oxygen<water<sugar.

Give reason for the following observations. (a) Naphthalene balls disappear with time without leaving any solid.

Question 3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Answer: (a) Naphthalene balls undergo sublimation due to which it converts directly into vapours and disappear into air without leaving any solid.
(b) The particles of perfume diffuse rapidly into the air and its smell can be felt while sitting several metres away.

Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C.

Question 2. Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
Answer: To concert Celsius scale into Kelvin scale we have to add 273 so    (a) 25 ºC=25+273=298K, (b) 373 ºC=373+273=646K

Convert the following temperatures to the Celsius scale. (a) 293 K (b) 470 K.

Question 1. Convert the following temperatures to the Celsius scale.
(a) 293 K (b) 470 K.
Answer: To concert Kelvin scale into Celsius scale we have to subtract 273 so (a) 293K=293-273=20 ºC, (b) 470K=470-273=197 ºC

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Question 3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer:  A diver is able to cut through water in a swimming pool this observation shows that the matter is made up of particles.

What are the characteristics of the particles of matter?

Question 4. What are the characteristics of the particles of matter?
Answer:  The characteristics of particles of matter are

(i) Particles of matter have spaces between them.
(ii) Particles of matter are continuously moving.
(iii) Particles of matter attract each other.
(iv) Kinetic energy of particles increases with increase in temperature.

Which of the following is matter?

Question 1. Which of the following is matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Answer: Chair, air, almonds and cold drink are matter.

Give reasons for the following observation: The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Question 2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer: The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close because the kinetic energy of the particles of matter increases with the increase in temperature.

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Quesiton 4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer: Ice in fact it is solid but it has cage like structure and hence its molecules have more empty space as compared to water so it has smaller density then water and hence floats on water.

Tabulate the differences in the characteristics of states of matter.

Question 2. (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following:
rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer: (a)

S.NO	Property	Solid	Liquid	Gases
1.	Shape	They Have definite shape	They do not have definite shape	They do not have definite shape
2.	Volume	They have definite volume	They do not have definite volume	They do not have definite volume
3.	Density	They have high density.	Liquids have less density than solids.	Liquids have least density.
4.	Kinetic energy of particles.	Least	More than solids	Maximum
5.	Compressibility	Negligible	Low	High

Rigidity: It is the property of matter to resist the change of its shape.
Compressibility: It is the property of matter in which its volume is decreased by applying force.
Fluidity: It is the ability of matter to flow.
Filling a gas container: On filling a gas takes the shape of the container.
Shape: Having definite boundaries.
Kinetic energy: It is the energy possessed by the particles of matter due to its motion.
Density: It is the ratio of mass with per unit volume

Give reasons (a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container.

Question 3. Give reasons                                                                                          
(a) A gas fills completely the vessel in which it is kept.                                
(b) A gas exerts pressure on the walls of the container.                              
(c) A wooden table should be called a solid.                                                
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer:

(a) A gas fills completely the vessel in which it is kept because the particles of gas move freely and acquire the shape of the container.
(b) A gas exerts pressure on the walls of the container because particles of gas move freely and randomly due to which they hit the boundaries of the container and exert the force on its wall.
(c) A wooden table has a definite shape and definite volume and hence it is called solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert because there is lot of empty space between the particles of gas but it not so in case of solids.

The mass per unit volume of a substance is called density.

Question 1. The mass per unit volume of a substance is called density. (Density = mass/volume).
Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer: Arrangement of the above matters in order of increasing density
Air<exhaust from chimney<cotton<water<honey<chalk<Iron

For any substance, why does the temperature remain constant during the change of state?

Quesiton 3. For any substance, why does the temperature remain constant during the change of state?
Answer: The temperature remain constant during the change of state because the heat supplied is used up in changing the state of matter as it has to work against the force of attraction of molecules.

Suggest a method to liquefy atmospheric gases.

Question 4. Suggest a method to liquefy atmospheric gases.
Answer: The gases can be converted into liquids by bringing its particles closer so atmospheric gases can be liquefied either by decreasing temperature or by increasing pressure.

Convert the following temperature to Celsius scale: a. 300 K b. 573 K.

Question1. Convert the following temperature to Celsius scale: a. 300 K b. 573 K.
Answer: To concert Kelvin scale into Celsius scale we have to subtract 273 so (a) 300K=300-273=27 ºC, (b) 573K=573-273=300 ºC

What is the physical state of water at: a. 250ºC, b. 100ºC?

Question 2. What is the physical state of water at: a. 250ºC, b. 100ºC?
Answer: (a) At 250ºC water exist in only gaseous state. (b) At 100ºC water exist in both gaseous and liquid state.

What type of clothes should we wear in summer?

Question 5. What type of clothes should we wear in summer?
Answer: During summer we should wear cotton cloths because they are good absorber of water. As Cotton cloths absorbs sweat rapidly resulting in higher rate of evaporation Due to which our body feels cool.   

Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Question 3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer: When we put some acetone, petrol or perfume it starts evaporating by using the energy from palm and leaving it cool.

Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Question 4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer:  We are able to sip tea, milk faster from a saucer because it has larger surface area than the cup, In larger surface area rate of evaporation is faster due to which tea or milk cools rapidly.

How does the water kept in an earthen pot (matka) become cool during summer?

Question 2. How does the water kept in an earthen pot (matka) become cool during summer?
Answer: The water kept in an earthen pot (matka) becomes cool during summer because of the evaporation of water through the fine holes in the earthen pot which makes it cool.

Why does a desert cooler cool better on a hot dry day?

Question 1. Why does a desert cooler cool better on a hot dry day?
Answer: A desert cooler cools better on a hot dry day because on a hot dry day temperature is high and humidity is less which helps in better evaporation. Due to the higher rate of evaporation it gives better cooling effect.

What are alloys?

Question 3. What are alloys?
Answer: An alloy is the homogeneous mixture of two or more metals or metals and non metals. For example brass is an alloy of copper and zinc.

Metallic oxides of zinc, magnesium and copper were heated with the following metals.

Quesiton 1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

In which cases will you find displacement reactions taking place?
Answer: On the basis of reactivity series of metals the displacement reaction will take place as follows

Which metals do not corrode easily?

Question 2. Which metals do not corrode easily?
Answer: Metals which have law reactivity such as silver, gold does not corrode easily. 

What chemical process is used for obtaining a metal from its oxide?

Question 3. What chemical process is used for obtaining a metal from its oxide?
Answer: A metal can be extracted from its oxide by the process of reduction

Define the following terms. (i) Mineral (ii) Ore (iii) Gangue

Question 1. Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
Answer: 
Mineral: The naturally occurring compounds of elements are known as Mineral. 
Ore: The mineral from which element can be extracted easily and profitably is called an ore.
Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.

Name two metals which are found in nature in the free state.

Question 2. Name two metals which are found in nature in the free state.
Answer: Gold and Platinum

Why do ionic compounds have high melting points?

Question 2. Why do ionic compounds have high melting points?
Answer: In an ionic compound there is large electrostatic force of attraction between opposite charged ions. To overcome these forces a considerable amount of energy is needed therefore ionic compounds have high melting points.

Write the electron-dot structures for sodium, oxygen and magnesium.

Question 1.(i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na₂O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
Answer: (i) 

(ii)

(iii)
Ions present in are Na₂O are Na⁺ and O^2-
Ions present in MgO are Mg²⁺ and O^2-

Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute sulphuric acid.

Question 4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute sulphuric acid.
Answer: Hydrogen gas is evolved when hydrochloric acid is added to a reactive metal. The chemical reaction when iron reacts with dilute sulphuric acid is

What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

Question 5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer: When zinc is added to iron (II) sulphate then it will displace the iron from iron sulphate solution as shown in the following chemical reaction

Samples of four metals A, B, C and D were taken

Question 3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.

(i)Which is the most reactive metal?
Answer: B is most reactive metal.

(ii) What would you observe if B is added to a solution of Copper (II) sulphate?
Answer: B will displace copper from copper sulphate.

(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer: Arrangement of metals in the order of decreasing reactivity B>A>C>D