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.