Chose the correct statements about interstitial compounds from the following:

(A) They have low melting points, lower than those of pure metals
(B) They are perfect-stoichiometric compounds
(C) These are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals
(D) They are neither typically ionic nor covalent

Choose the correct answer from the options given below:

(C) and (D) only

The correct answer is Option (2) → (C) and (D) only

(A) They have low melting points... (FALSE): Interstitial compounds actually have very high melting points, often higher than those of the pure parent metals. This is because the trapped atoms increase the strength of the metallic bonding.

(B) They are perfect-stoichiometric compounds (FALSE): These are typically non-stoichiometric compounds. Their compositions cannot be expressed by simple whole-number ratios (e.g., $TiH_{1.7}$, $VH_{0.56}$).

(C) Formation from small atoms (TRUE): They are formed when small atoms like Hydrogen, Carbon, or Nitrogen occupy the vacant spaces (interstices) within the crystal lattice of a transition metal.

(D) Neither typically ionic nor covalent (TRUE): The bonding in these compounds does not follow the standard rules of ionic or covalent bonding. They retain metallic conductivity and luster but become much harder and more brittle.