Question

In which of the following, the identity of initial substance remains unchanged?

Options

• Curdling of milk

• Formation of crystals by process of crystallisation

• Fermentation of grapes

• Digestion of food

Answer 1

Formation of crystals by process of crystallisation

Explanation:

Crystallisation is a physical change, the substance only changes its state/arrangement (forms a solid lattice) but its chemical identity stays the same. Curdling, fermentation and digestion are chemical changes where new substances (changed proteins, acids/alcohols, or breakdown products) are formed.