Consider the following types of hydrides
1. Covalent hydride
2. Ionic hydride
3. Metallic hydride
Which of these are formed by hydrogen?

Options

A. 1 and 2
B. 1 and 3
C. 2 and 3
D. All of these

Explanation

To determine which types of hydrides are formed by hydrogen, we will analyze each type of hydride mentioned in the question: covalent hydride, ionic hydride, and metallic hydride.

### Step-by-Step Solution:

1. **Covalent Hydride**:
- Covalent hydrides are formed when hydrogen reacts with elements that have similar electronegativity. In these compounds, hydrogen shares electrons with the other element, resulting in covalent bonds.
- **Example**: Methane (CH₄) is a classic example of a covalent hydride, where hydrogen bonds covalently with carbon.

2. **Ionic Hydride**:
- Ionic hydrides are formed when hydrogen reacts with S-block elements (alkali and alkaline earth metals). In these cases, hydrogen typically gains an electron to form a hydride ion (H⁻), resulting in ionic bonding.
- **Example**: Sodium hydride (NaH) is an example of an ionic hydride, where sodium donates an electron to hydrogen.

3. **Metallic Hydride**:
- Metallic hydrides are formed when hydrogen bonds with metals, particularly transition metals. In these compounds, hydrogen can exist in a metallic lattice, often exhibiting properties similar to metals.
- **Example**: Aluminum hydride (AlH₃) and magnesium hydride (MgH₂) are examples of metallic hydrides, where hydrogen interacts with metal elements.

### Conclusion:
Based on the analysis:
- Hydrogen can form **Covalent Hydrides**, **Ionic Hydrides**, and **Metallic Hydrides**.

Thus, all three types of hydrides mentioned in the question are formed by hydrogen.