Which of the following metals do not combine directly with hydrogen gas to form hydride?

Options

A. Mg
B. Ca
C. Be
D. Sr

Answer

To determine which metal does not combine directly with hydrogen gas to form a hydride, we can analyze the behavior of various metals with hydrogen.

### Step-by-Step Solution:

1. **Understanding Hydrides**: Hydrides are compounds formed when metals react with hydrogen. The general formula for hydrides of alkaline earth metals is MH2, where M represents the metal.

2. **Identify the Metals**: The metals in question are typically from groups such as the alkaline earth metals (Group 2) and other metals that might react with hydrogen.

3. **Reactivity with Hydrogen**:
- Common alkaline earth metals include magnesium (Mg), calcium (Ca), strontium (Sr), and beryllium (Be).
- Most of these metals readily react with hydrogen to form their respective hydrides.

4. **Analyzing Beryllium**:
- Beryllium is unique among the alkaline earth metals because it does not react directly with hydrogen to form a hydride under normal conditions.
- Instead, beryllium forms a hydride only under specific conditions or through indirect methods.

5. **Conclusion**: Based on the reactivity of these metals with hydrogen, we conclude that beryllium (Be) does not combine directly with hydrogen gas to form a hydride.

### Final Answer:
The metal that does not combine directly with hydrogen gas to form a hydride is **Beryllium (Be)**.

---