Which of the following statements is correct ?

Options

A. Metallic hydrides are deficient of hydrogen?
B. Metallic hydrides conduct heat and electricity
C. Ionic hydrides do not conduct electricity in solid state.
D. Ionic hydrides are very good conductors of electricity in solid state.

Explanation

To determine which of the statements regarding metallic hydrides and ionic hydrides is correct, we can analyze each statement based on the properties of these compounds.

### Step-by-Step Solution:

1. **Understanding Metallic Hydrides**:
- Metallic hydrides are formed when metals react with hydrogen. They are typically non-stoichiometric, meaning they do not have a fixed ratio of metal to hydrogen.
- Non-stoichiometric hydrides are hydrogen-deficient compounds, which means they contain less hydrogen than would be expected based on a simple formula.

**Hint**: Remember that metallic hydrides are often formed from transition metals and can vary in composition.

2. **Properties of Metallic Hydrides**:
- Metallic hydrides can conduct heat and electricity due to the presence of metallic bonds and free electrons.
- This property is significant because it distinguishes them from other types of hydrides.

**Hint**: Consider the role of metallic bonds in conductivity.

3. **Understanding Ionic Hydrides**:
- Ionic hydrides are formed between hydrogen and highly electropositive metals (like alkali and alkaline earth metals).
- In solid form, ionic hydrides do not conduct electricity because the ions are fixed in place within the crystal lattice and cannot move freely.

**Hint**: Think about how ionic compounds behave in solid versus liquid states.

4. **Conductivity of Ionic Hydrides**:
- Ionic hydrides can conduct electricity when they are in an aqueous solution or molten state because the ions are free to move.
- Therefore, they are good conductors of electricity in these states, but not in solid form.

**Hint**: Recall that conductivity in ionic compounds requires mobile ions.

5. **Evaluating the Statements**:
- **Statement 1**: Metallic hydrides are non-stoichiometric and hydrogen-deficient. (True)
- **Statement 2**: Metallic hydrides can conduct heat and electricity. (True)
- **Statement 3**: Ionic hydrides do not conduct electricity in solid states. (True)
- **Statement 4**: Ionic hydrides are very good conductors of electricity in solid states. (False)

**Hint**: Compare the properties of metallic and ionic hydrides to identify the correct statements.

### Conclusion:
Based on the analysis, the correct statements are:
- Metallic hydrides are non-stoichiometric and hydrogen-deficient.
- Metallic hydrides can conduct heat and electricity.
- Ionic hydrides do not conduct electricity in solid states.

Thus, the correct options are 1, 2, and 3.