Pure substances in the given list of materials are :
(a) Ice (compound) (c ) Iron (element) (e) Calcium oxide (compound) (f) Mercury (element).
Both milk and hydrochloric acid are homogeneous mixtures. Please note that the acid is formed when the vapours of hydrogen chloride gas are passed through water.
Wood and air (containing suspended particles) are heterogeneous mixtures. However, air free from any suspended particles is a homogeneous mixture.
