Mention the type of compounds formed when small atoms like $H$,$C$ and $N$ get trapped inside the crystal lattice of transition metals. Also,give the physical and chemical characteristics of these compounds.

(N/A) The compounds formed are known as interstitial compounds. These are formed when small atoms like $H$,$B$,$C$,and $N$ are trapped inside the interstitial sites of the crystal lattice of transition metals.
The physical and chemical characteristics are:
$(i)$ They have high melting points,which are even higher than those of pure transition metals.
$(ii)$ They are extremely hard; some borides approach diamond in hardness.
$(iii)$ They retain metallic conductivity.
$(iv)$ They are chemically inert.