If a gas expands through a volume of 100mL against atmospheric pressure, the work done by the gas `= "…................"` joule .

Explanation

To calculate the work done by the gas when it expands against atmospheric pressure, we can use the formula:

\[ W = P_{\text{external}} \times \Delta V \]

Where:
- \( W \) is the work done,
- \( P_{\text{external}} \) is the external pressure (atmospheric pressure),
- \( \Delta V \) is the change in volume.
...