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

Explanation

To prepare hydrogen from water (H₂O), we need to identify a suitable reducing agent. Here’s a step-by-step solution to the question:

### Step 1: Understanding the Reaction
Hydrogen (H₂) can be produced from water (H₂O) through a chemical reaction where water is reduced. In this context, reduction refers to the gain of electrons, which decreases the oxidation state of hydrogen from +1 in water to 0 in molecular hydrogen (H₂).

### Step 2: Identifying the Reducing Agent
To facilitate this reduction, we need a reducing agent. A reducing agent is a substance that donates electrons to another substance, thereby reducing it. In this case, we are looking for a metal that can donate electrons to water.

### Step 3: Evaluating the Options
From the video transcript, the options mentioned include:
- Calcium (Ca)
- Aluminum (Al)
- Silver (Ag)
- Gold (Au)

Among these, we need to determine which of these metals can act as a reducing agent for water.

### Step 4: Reactivity Series
In the reactivity series of metals, metals that are higher than hydrogen can displace hydrogen from water. Calcium and aluminum are both above hydrogen in the reactivity series, making them suitable candidates for acting as reducing agents.

### Step 5: Reaction with Water
When calcium reacts with water, the reaction can be represented as:
\[ \text{Ca} + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2 \uparrow \]
This shows that calcium donates electrons to water, reducing it and producing hydrogen gas.

### Conclusion
Therefore, the correct answer to the question is that hydrogen is prepared from water by adding **calcium (Ca)**, which acts as a reducing agent.

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