(a) Identify the test tube(s) in which a chemical change take place.
(b) Does the molecular composition remain the same in all the test tubes?

Explanation

(a) In test tube-C chemical change takes place. Calcium oxide dissolves in water to form calcium hydroxide. This process is called slaking of lime and is applicable in white washing of buildings.
(b) Addition of sugar or common salt to water is a physical change. The composition remains the same in test tubes A and B.