Question

Which of the following statements about the interstitial compounds is incorrect?
(A)- They retain metallic conductivity
(B)- They are chemically reactive
(C)- They are much harder than the pure metal
(D)- They have higher melting points than the pure metal

Answer 1

Hint: The non-stoichiometric transition metal compounds which have voids present in them in their crystal lattice. These can be occupied by the small atoms, such that they remain chemically inert.

Complete step by step solution:
The compounds in which the metals crystal lattice has small atoms trapped within it, are known as the interstitial compounds. The transition metals with high atomic number and large atomic size, have voids present in its crystal structure, which are often occupied by the small atoms like the H, N, C and B atoms. Hence, form the interstitial compounds.
The presence of these small atoms in their interstitial sites makes the compounds non-stoichiometric as its definite proportion cannot be determined in the form of a well-defined number. Also, making it chemically inert. Thus, having no effect on its chemical properties of the transition parent metal and retain its conductivity and reactivity.
Whereas, due to its occupancy in the voids, it does enhance the physical properties of the compound. such as its density, hardness, malleability, ductility. Also, due to the bonding between the interstitial atoms and the transition metals it increases its melting and boiling point compared to the parent metal.

Therefore, the incorrect statement is option (B) the interstitial compounds are chemically reactive.

Note: A common example of interstitial compound is the crystal lattice of iron, having the carbon atoms in the voids present in it, that is, $F{{e}_{3}}C$, that plays a crucial role in the properties of steel. As during the formation, the malleability and ductility of the iron metal decreases, but the compound formed has higher tenacity.