The correct answer is Option (1) → (A), (C) and (D) only
Based on the properties of interstitial compounds formed by transition metals, here is the evaluation of the statements:
- (A) Have higher melting points than those of pure metals: Correct. The presence of small atoms in the lattice sites often strengthens the bonding (creating metal-nonmetal interactions), which leads to significantly higher melting points compared to the parent pure metals.
- (B) Have more reactivity than those of pure metals: Incorrect. Interstitial compounds are generally chemically inert and less reactive than pure metals. For example, many transition metal carbides are extremely resistant to chemical attack.
- (C) Are non-stoichiometric compounds: Correct. These compounds usually do not follow simple valency rules or fixed ratios (e.g., $TiH_{1.7}$, $VH_{0.56}$), as the number of available interstitial holes occupied can vary.
- (D) Formed when small atoms like H, C or N are trapped inside the crystal lattice of the metals: Correct. This is the fundamental definition of an interstitial compound; small atoms occupy the octahedral or tetrahedral "voids" in the metal's packed structure.
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