Question

Which of the following is NOT a physical or chemical characteristic of interstitial compounds?

• A. They have high melting points, higher than those of pure metals.
• B. They are very soft and ionic in nature.
• C. They retain metallic conductivity.
• D. They are chemically inert and usually non-stoichiometric.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The topic is the Chemistry of d-Block Elements.
We are asked to identify which statement incorrectly describes the properties of interstitial compounds. These are compounds formed when small non-metal atoms get trapped in the lattice of a transition metal.
Step 2: Detailed Explanation:
Let's evaluate the properties of interstitial compounds against the given options:
(A) They have high melting points, higher than those of pure metals.
This is a correct statement. The strong interactions between the trapped non-metal atoms and the metal atoms strengthen the crystal lattice, leading to very high melting points.
(B) They are very soft and ionic in nature.
This is an incorrect statement. Interstitial compounds are known for being extremely hard and rigid (e.g., tungsten carbide, titanium nitride). The bonding is primarily metallic with some covalent character, not ionic. Therefore, this statement is false.
(C) They retain metallic conductivity.
This is a correct statement. The metallic bonding character and the 'sea of electrons' from the parent metal are largely preserved, allowing them to conduct electricity.
(D) They are chemically inert and usually non-stoichiometric.
This is a correct statement. The filling of the interstitial sites makes the compounds more stable and less reactive. They are also famous for being non-stoichiometric, meaning their chemical formulas do not correspond to simple integer ratios (e.g., \(TiH_{1.7}\)).
Since the question asks for the characteristic that is NOT a property, the answer is (B).
Step 3: Final Answer:
The statement "(B) They are very soft and ionic in nature" is NOT a characteristic of interstitial compounds.