On heating a sample, water droplets appear and its colour changes. This may identify what kind of salt?

Correct answer: Salt containing water of crystallisation

The governing concept is water of crystallisation: a fixed number of water molecules incorporated into the crystal structure of some salts. On heating, this water may be released as droplets or vapour, and removal can alter the crystal structure and colour. For example, hydrated copper sulphate is blue and becomes white on losing water. A salt cannot be defined as ion-free or always gaseous. Thus option A is correct.