Interstitial compounds are formed when small atoms like H, C, or N are trapped in the crystal lattice of metal. Which of the following statements are true about the interstitial compounds?
(A) Interstitial compounds have higher melting points than the pure metals.
(B) Interstitial compounds are very soft.
(C) Interstitial compounds are very reactive.
(D) Interstitial compounds retain metallic conductivity.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (D) 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. The small atoms lock the metal atoms in place, which makes the lattice harder and more rigid, while the metallic bonding of the host remains.
(A) Interstitial compounds have higher melting points than the pure metals. — Correct. The extra bonding between the metal and the trapped atoms makes the lattice more rigid, so more energy is needed to melt it.
(B) Interstitial compounds are very soft. — Incorrect. They are very hard; some borides approach diamond in hardness.
(C) Interstitial compounds are very reactive. — Incorrect. They are chemically inert, because the small atoms are held firmly in the metal lattice.
(D) Interstitial compounds retain metallic conductivity. — Correct. The metal lattice and its mobile electrons are still there, so they conduct like metals.
NCERT (2026-27 edition):
Formation of Interstitial Compounds
