Consider the following statements about the physical and chemical characteristics of interstitial compounds and identify the correct statements
(A) They have high melting points.
(B) They are very hard.
(C) They retain metallic conductivity.
(D) They are chemically very reactive.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
Interstitial compounds are formed when small atoms such as H, C or N are trapped in the spaces of the crystal lattice of a transition metal, as in TiC, \( \ce{Mn4N} \) and \( \ce{Fe3H} \). They are usually non-stoichiometric and neither typically ionic nor covalent. The small atoms lock the metal layers in place.
(A) They have high melting points. — Correct. Their melting points are higher even than those of the pure metals.
(B) They are very hard. — Correct. The trapped atoms stop the metal layers from sliding; some borides approach diamond in hardness.
(C) They retain metallic conductivity. — Correct. The metal lattice, with its free electrons, is still there.
(D) They are chemically very reactive. — Incorrect. Interstitial compounds are chemically inert.
NCERT (2026-27 edition):
Formation of Interstitial Compounds – “Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. … The principal physical and chemical characteristics of these compounds are as follows:
(i) They have high melting points, higher than those of pure metals.
(ii) They are very hard, some borides approach diamond in hardness.
(iii) They retain metallic conductivity.
(iv) They are chemically inert.”