The correct statement about sodium and its compounds would include that:

Options

A. Sodium forms an ionic hydride NaH
B. Sodium nitrate decomposes to the nitrite on heating
C. Sodium is hard metal
D. Sodium carbonate decomposes readily on heating

Answer

To solve the question regarding the correct statements about sodium and its compounds, we will analyze each option provided.

### Step-by-Step Solution:

1. **Evaluate Option 1: Sodium forms an ionic hydride NaH.**
- Sodium (Na) is a soft metal that reacts with hydrogen gas at elevated temperatures (around 200°C) to form sodium hydride (NaH).
- Sodium hydride is indeed ionic in nature due to the transfer of an electron from sodium to hydrogen, resulting in Na⁺ and H⁻ ions.
- **Conclusion:** This statement is correct.

2. **Evaluate Option 2: Sodium nitrate decomposes to the nitrite on heating.**
- When sodium nitrate (NaNO₃) is heated above 800°C, it decomposes to form sodium nitrite (NaNO₂) and oxygen gas (O₂).
- The reaction can be represented as:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- **Conclusion:** This statement is also correct.

3. **Evaluate Option 3: Sodium is a hard metal.**
- Sodium is classified as a soft metal. It is malleable and can be easily cut with a knife.
- **Conclusion:** This statement is incorrect.

4. **Evaluate Option 4: Sodium carbonate decomposes readily on heating.**
- Sodium carbonate (Na₂CO₃) is stable and does not decompose readily upon heating. It requires very high temperatures to decompose, and even then, the decomposition is not considered "readily."
- **Conclusion:** This statement is incorrect.

### Final Conclusion:
The correct statements about sodium and its compounds are:
- Sodium forms an ionic hydride NaH.
- Sodium nitrate decomposes to the nitrite on heating.