Give balanced equations to show the preparation of hydrogen by the following:
cold water.

Explanation

To prepare hydrogen gas using cold water, we can react sodium (Na) with water (H2O). Here’s the step-by-step solution to balance the equation for this reaction:

### Step 1: Write the unbalanced equation
The initial reaction can be written as:
\[ \text{Na} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \]

### Step 2: Count the number of atoms on both sides
- On the left side, we have:
...