In which of the compounds does hydrogen have an oxidation state of -1 ?

Options

A. `CH_(4)`
B. `NH_(3)`
C. HCl
D. `CaH_(2)`

Answer

To determine in which of the given compounds hydrogen has an oxidation state of -1, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Identify the Compounds:**
We have four compounds to analyze:
- CH₄ (Methane)
- NH₃ (Ammonia)
- HCl (Hydrochloric acid)
- CaH₂ (Calcium hydride)

2. **Analyze CH₄ (Methane):**
- In CH₄, carbon (C) is more electronegative than hydrogen (H).
- Therefore, hydrogen has an oxidation state of +1.
- **Conclusion:** CH₄ does not have hydrogen in the -1 oxidation state.

3. **Analyze NH₃ (Ammonia):**
- In NH₃, nitrogen (N) is more electronegative than hydrogen.
- Thus, hydrogen again has an oxidation state of +1.
- **Conclusion:** NH₃ does not have hydrogen in the -1 oxidation state.

4. **Analyze HCl (Hydrochloric Acid):**
- In HCl, chlorine (Cl) is more electronegative than hydrogen.
- Hence, hydrogen has an oxidation state of +1.
- **Conclusion:** HCl does not have hydrogen in the -1 oxidation state.

5. **Analyze CaH₂ (Calcium Hydride):**
- In CaH₂, calcium (Ca) is a metal and is less electronegative than hydrogen.
- Therefore, hydrogen has an oxidation state of -1 in this compound.
- **Conclusion:** CaH₂ has hydrogen in the -1 oxidation state.

### Final Answer:
The compound in which hydrogen has an oxidation state of -1 is **CaH₂ (Calcium Hydride)**.

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