Which of the following statements about the interstitial compounds is incorrect?

Question

Accepted Answer

Interstitial compounds are formed when small atoms like hydrogen, carbon, or nitrogen occupy the interstitial spaces in a metal lattice. Let's analyze each option to understand why Option 3 is the correct answer:

1. **They have higher melting points than the pure metal.**  
   Interstitial compounds generally have higher melting points compared to the pure metals from which they are formed. This is because the presence of small atoms in the interstitial spaces strengthens the metallic lattice, making it more difficult to break apart. Therefore, this statement is correct and not the incorrect one.

2. **They retain metallic conductivity.**  
   Interstitial compounds typically retain the metallic conductivity of the parent metal. The presence of interstitial atoms does not significantly disrupt the electron sea that is responsible for metallic conductivity. Thus, this statement is also correct.

3. **They are chemically reactive.**  
   This statement is incorrect, which is why it is the correct answer to the question. Interstitial compounds are generally less chemically reactive than the pure metals. The small atoms in the interstitial spaces often stabilize the metal lattice, making it less prone to chemical reactions. This reduced reactivity is a characteristic feature of interstitial compounds.

4. **They are much harder than pure metal.**  
   Interstitial compounds are indeed much harder than the pure metals from which they are formed. The introduction of small atoms into the metal lattice increases the hardness by preventing the layers of metal atoms from sliding over each other easily. Therefore, this statement is correct.

In conclusion, Option 3 is the correct answer because it is the only statement that inaccurately describes a property of interstitial compounds.