The correct statement about interstitial compound is

Options

A. Interstitial compound are formed by small atoms such as `C,N,H,B` etc .
B. These compounds are nonstoichiometric
C. They show difference in physical properties but similarity in chemical properties
D. All of these

Answer

To solve the question regarding the correct statement about interstitial compounds, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Interstitial Compounds**:
- Interstitial compounds are formed when small atoms occupy the interstitial voids (empty spaces) in the lattice structure of larger metal atoms, typically transition metals from the D or F block of the periodic table.

2. **Formation of Interstitial Compounds**:
- These compounds are primarily formed by transition elements. The small atoms that can occupy the interstitial spaces include carbon, hydrogen, boron, and nitrogen.

3. **Characteristics of Interstitial Compounds**:
- **Non-stoichiometric Nature**: The ratio of the metal to the small atom in interstitial compounds is not fixed, meaning they can exist in various ratios. For example, compounds like TiC and TiH2 can have different stoichiometries such as TiH1.7 or VH0.56.
- **Bonding**: The bonding in interstitial compounds is neither purely ionic nor purely covalent, which contributes to their unique properties.

4. **Physical and Chemical Properties**:
- Interstitial compounds exhibit different physical properties compared to the pure metals they are derived from. They tend to be very hard and rigid (e.g., steel is an interstitial compound of iron and carbon).
- However, their chemical properties are often similar to those of the pure metals.

5. **Conclusion**:
- Based on the characteristics discussed, we can conclude that:
- They are formed by small atoms.
- They are non-stoichiometric.
- They show differences in physical properties but similarities in chemical properties.

6. **Final Answer**:
- Therefore, the correct statement about interstitial compounds is that all the provided statements are correct.