(i) Olfactory indicator: Substances whose odour changes in acidic or basic media are called olfactory indicators. Examples: onion, vanilla essence, clove oil.
(ii) Water of crystallisation: The fixed number of water molecules present in one formula unit of a salt is called water of crystallisation. Example: CuSO₄·5H₂O.
Source: Acids, Bases and Salts, sections 2.1.1 and "What you have learnt"
For olfactory indicators, the key phrase from the textbook is "substances whose odour changes in acidic or basic media." Always give an example.
For water of crystallisation, copy the textbook definition exactly — "fixed number of water molecules present in one formula unit of a salt." An example (like blue vitriol) earns full marks. Since this is a 1-mark question split into two parts, each definition needs just one concise line.