Assertion :- Oxidation state of Hydrogen is `+1` in `H_(2)O` while `-1` in `CaH_(2)`.
Reason :- `CaH_(2)` is a metal hydride and for metal hydrides, hydrogen is assigned the oxidation number of `-1`.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that the oxidation state of hydrogen is +1 in H₂O and -1 in CaH₂.

1. **Calculate the oxidation state of hydrogen in H₂O:**
- In H₂O, we have 2 hydrogen atoms and 1 oxygen atom.
- Let the oxidation state of hydrogen be \( x \).
- The oxidation state of oxygen is typically -2.
- The equation can be set up as:
\[ 2x + (-2) = 0 \]
- Solving for \( x \):
\[ 2x - 2 = 0 \\ 2x = 2 \\ x = +1 \]
- Therefore, the oxidation state of hydrogen in H₂O is +1.

2. **Calculate the oxidation state of hydrogen in CaH₂:**
- In CaH₂, we have 2 hydrogen atoms and 1 calcium atom.
- Let the oxidation state of hydrogen be \( y \).
- The oxidation state of calcium is +2.
- The equation can be set up as:
\[ 2y + (+2) = 0 \]
- Solving for \( y \):
\[ 2y + 2 = 0 \\ 2y = -2 \\ y = -1 \]
- Therefore, the oxidation state of hydrogen in CaH₂ is -1.

### Conclusion for Assertion
The assertion is true: the oxidation state of hydrogen is +1 in H₂O and -1 in CaH₂.

### Step 2: Analyze the Reason
The reason states that CaH₂ is a metal hydride and for metal hydrides, hydrogen is assigned an oxidation number of -1.

1. **Understanding Metal Hydrides:**
- Metal hydrides are compounds formed between metals and hydrogen.
- In these compounds, hydrogen typically has an oxidation state of -1.

2. **Check the validity of the reason:**
- Since CaH₂ is indeed a metal hydride (calcium being a metal), the statement that hydrogen has an oxidation number of -1 in metal hydrides is correct.

### Conclusion for Reason
The reason is also true: CaH₂ is a metal hydride, and in such compounds, hydrogen is assigned an oxidation number of -1.

### Final Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion.

### Answer
The correct answer is: **Both the assertion and reason are true, and the reason is the correct explanation of the assertion.**