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 of the given metals do not combine directly with hydrogen gas to form hydride, we will analyze the properties of each metal listed in the options.

### Step-by-Step Solution:

1. **Identify the Metals**: The metals provided in the question are:
- Option 1: Magnesium (Mg)
- Option 2: Calcium (Ca)
- Option 3: Beryllium (Be)
- Option 4: Strontium (Sr)

2. **Understand the Group**: All these metals belong to Group 2 of the periodic table, known as alkaline earth metals.

3. **General Reaction of Alkaline Earth Metals with Hydrogen**:
- Alkaline earth metals typically react with hydrogen gas (H₂) when heated to form hydrides with the general formula MH₂, where M represents the metal.
- For example:
- Magnesium + Hydrogen → Magnesium Hydride (MgH₂)
- Calcium + Hydrogen → Calcium Hydride (CaH₂)
- Strontium + Hydrogen → Strontium Hydride (SrH₂)

4. **Examine Beryllium**:
- Beryllium is unique among the alkaline earth metals. It does not react directly with hydrogen gas to form beryllium hydride (BeH₂) under normal conditions.
- Instead, beryllium hydride can be prepared through other methods, such as the reduction of beryllium chloride (BeCl₂) with lithium aluminum hydride (LiAlH₄).

5. **Conclusion**:
- From the analysis, we find that while magnesium, calcium, and strontium can directly combine with hydrogen to form their respective hydrides, beryllium does not. Therefore, the metal that does not combine directly with hydrogen gas to form a hydride is **Beryllium (Be)**.

### Final Answer:
**Option 3: Beryllium (Be)**