(a) Optical activity : The phenomenon or property pf organic substances 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 HH are trapped inside the interstitial space in crystal of metals.