Q.

The compounds in which small atoms such as H,B,N,C occupy the interstitial spaces in the
lattice of any metal are called interstitial compounds.
Transitional elements forms a few interstitial compounds with elements having small atomic
radii such as H,B,N,C. The small atoms of these elements get enter in between the empty spaces of the metal lattice.
Ex: TiC, FeO, TiN