Interstitial compounds are formed when small atoms are dropped under the curved lattice of metals. Whether the following is not the characteristics property of interstitial compounds?

Options

A. They have high melting points in to pure metals
B. They are very hard
C. They retain metallic conductivity
D. They are chemically very reactive

Explanation

To determine which of the following is not a characteristic property of interstitial compounds, we will analyze each option based on the properties of interstitial compounds.

### Step-by-Step Solution:

1. **Understanding Interstitial Compounds**:
Interstitial compounds are formed when small atoms (like carbon, nitrogen, or boron) occupy the interstitial spaces (the gaps) in the metallic lattice structure of metals. These compounds typically exhibit unique properties due to the presence of both metal and non-metal atoms.

2. **Analyzing the Properties**:
- **High Melting Points**: 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 lattice increases the overall bonding strength.
- **Hardness**: Interstitial compounds are typically very hard. For example, steel (an interstitial compound of iron and carbon) is much harder than pure iron.
- **Metallic Conductivity**: These compounds often retain metallic conductivity due to the metallic nature of the host metal, even though they contain non-metal atoms.
- **Chemical Reactivity**: Interstitial compounds tend to be less chemically reactive compared to their constituent metals. The presence of small atoms can stabilize the structure, making them less reactive.

3. **Identifying the Incorrect Statement**:
- The statement "they are chemically very reactive" is not true for interstitial compounds. In fact, they are usually less reactive than the pure metals. Therefore, this statement does not characterize interstitial compounds.

4. **Conclusion**:
The property that is not characteristic of interstitial compounds is that "they are chemically very reactive."

### Final Answer:
The correct answer is that interstitial compounds are **not** characterized by being chemically very reactive.