Hydrogen is prepared from `H_(2)O` by adding

Options

A. Ca, which acts as reducing agent
B. Al. which acts as oxidising agent
C. Ag. Which acts as reducing agent
D. Au. Which acts as oxidising agent

Answer

To solve the question of how hydrogen is prepared from water (H₂O) by adding a certain element, we will analyze the options provided and determine which one is correct based on the principles of redox reactions.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- Hydrogen gas can be produced from water when a more reactive element displaces hydrogen from water. The general reaction can be represented as:
\[ \text{X} + \text{H}_2\text{O} \rightarrow \text{XOH} + \text{H}_2 \]
- Here, X is the element that will react with water to produce hydrogen gas (H₂).

2. **Identifying the Role of X**:
- In this reaction, X must act as a reducing agent. A reducing agent is a substance that donates electrons to another substance, reducing its oxidation state. In this case, X reduces the oxidation state of hydrogen from +1 in water to 0 in hydrogen gas.

3. **Checking Reactivity**:
- For X to successfully displace hydrogen from water, it must be more reactive than hydrogen. The reactivity series of metals indicates that more reactive metals can displace less reactive metals from their compounds.

4. **Analyzing the Options**:
- **Option 1: Calcium (Ca)**: Calcium is indeed more reactive than hydrogen and acts as a reducing agent. This option is correct.
- **Option 2: Aluminum (Al)**: While aluminum is more reactive than hydrogen, it acts as an oxidizing agent in some reactions, which makes this option incorrect.
- **Option 3: Silver (Ag)**: Silver is less reactive than hydrogen, so it cannot displace hydrogen from water. This option is incorrect.
- **Option 4: Gold (Au)**: Gold is also less reactive than hydrogen, making this option incorrect.

5. **Conclusion**:
- The only correct option is **Calcium (Ca)**, which acts as a reducing agent and is more reactive than hydrogen, allowing it to liberate hydrogen gas from water.

### Final Answer:
Hydrogen is prepared from H₂O by adding **Calcium (Ca)**, which acts as a reducing agent.

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