Explain the terms:
(a) Optical activity (b) Ligand
(c ) Interstitial compounds.

Explanation

(a) Optical activity : The phenomenon or property or organic substance to rotate the plane of PPL towards right or left is called as optical activity.
(b) Ligand : The molecule or ion which are coordinated to the metal atom or ion in coordination compound are called as ligands
(c ) Interstitial compounds : Those compounds which are formed when small amount of small atoms like H, C and N are trapped inside the interstitial space in crystal of metals.