Which of the following reaction is reaction is used to make a fuel cell .

Options

A. `Cd_(s)+2Ni(OH)_(3(s)) to CdO_(s) + 2Ni(OH)_(2(s)) + H_2O_(l)`
B. `Pb_(s) + PbO_(2(s)) + 2H_2SO_(4(aq)) to 2PbSO_(4(s)) + 2H_2O_(l)`
C. `2H_(2(g)) + O_(2(g)) to 2H_2O_(l)`
D. `2Fe(s) + O_(2(g)) + 4H_(aq)^(+) to 2Fe_(aq)^(2+) + 2H_2O_(l)`

Explanation

To determine which reaction is used to make a fuel cell, we need to analyze the electrochemical process involved in a fuel cell. A fuel cell typically involves the reaction between hydrogen and oxygen to produce water, along with the generation of electricity.

### Step-by-Step Solution:

1. **Understanding Fuel Cells**:
- A fuel cell is a device that converts chemical energy directly into electrical energy through an electrochemical reaction.

2. **Identifying the Key Reactants**:
- The primary reactants in a hydrogen fuel cell are hydrogen (H2) and oxygen (O2).

3. **Electrochemical Reactions**:
- In a hydrogen fuel cell, the reactions occur at two electrodes: the anode and the cathode.
- At the **anode**, hydrogen gas is oxidized:
\[ 2H_2 \rightarrow 4H^+ + 4e^- \]
- At the **cathode**, oxygen is reduced:
\[ O_2 + 4H^+ + 4e^- \rightarrow 2H_2O \]

4. **Overall Reaction**:
- Combining the half-reactions gives the overall reaction for the fuel cell:
\[ 2H_2 + O_2 \rightarrow 2H_2O + \text{energy} \]
- This reaction shows that hydrogen and oxygen produce water and release energy, which is the principle behind fuel cells.

5. **Evaluating Options**:
- Now, we look at the provided options:
- **Option A**: Cadmium and nickel - Incorrect, as these are not the reactants used in a fuel cell.
- **Option B**: Pb and PbO2 - Incorrect, as this does not involve hydrogen and oxygen.
- **Option C**: \(2H_2 + O_2 \rightarrow 2H_2O\) - Correct, as this is the reaction used in fuel cells.
- **Option D**: Iron (Fe) - Incorrect, as iron is not involved in the basic hydrogen-oxygen fuel cell reaction.

6. **Conclusion**:
- The correct answer is **Option C**: \(2H_2 + O_2 \rightarrow 2H_2O\).