In which of the compounds the oxidation state of hydrogen is -1?

Options

A. `H_2O`
B. `CaH_2`
C. `HBr`
D. `H_2S`

Answer

To determine in which compound the oxidation state of hydrogen is -1, we will analyze the oxidation states of hydrogen in each of the given compounds: H2O, CH2, HBr, and H2S.

### Step-by-Step Solution:

1. **Analyze H2O (Water)**:
- The oxidation state of oxygen (O) is -2.
- Let the oxidation state of hydrogen (H) be \( x \).
- The equation becomes:
\[ 2x + (-2) = 0 \]
- Simplifying gives:
\[ 2x - 2 = 0 \implies 2x = 2 \implies x = +1 \]
- **Conclusion**: In H2O, the oxidation state of hydrogen is +1.

2. **Analyze CH2 (Calcium Hydride)**:
- Calcium (Ca) is a metal and typically has an oxidation state of +2.
- Let the oxidation state of hydrogen (H) be \( x \).
- The equation becomes:
\[ 2x + 2 = 0 \]
- Simplifying gives:
\[ 2x + 2 = 0 \implies 2x = -2 \implies x = -1 \]
- **Conclusion**: In CH2, the oxidation state of hydrogen is -1.

3. **Analyze HBr (Hydrogen Bromide)**:
- Bromine (Br) is more electronegative than hydrogen and typically has an oxidation state of -1.
- Let the oxidation state of hydrogen (H) be \( x \).
- The equation becomes:
\[ x + (-1) = 0 \]
- Simplifying gives:
\[ x - 1 = 0 \implies x = +1 \]
- **Conclusion**: In HBr, the oxidation state of hydrogen is +1.

4. **Analyze H2S (Hydrogen Sulfide)**:
- Sulfur (S) typically has an oxidation state of -2.
- Let the oxidation state of hydrogen (H) be \( x \).
- The equation becomes:
\[ 2x + (-2) = 0 \]
- Simplifying gives:
\[ 2x - 2 = 0 \implies 2x = 2 \implies x = +1 \]
- **Conclusion**: In H2S, the oxidation state of hydrogen is +1.

### Final Conclusion:
After analyzing all the compounds, we find that the oxidation state of hydrogen is -1 only in **CH2 (Calcium Hydride)**.

### Answer:
The compound in which the oxidation state of hydrogen is -1 is **CH2 (Calcium Hydride)**.

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