Solution:
Given that;
If the gas and piston has volume of 20.0L at a temperature of 25°C
To find the volume of the gas when heated tom 100°C, we will apply Charles law formula, which is
[tex]\begin{gathered} \frac{V_1}{T_1}=\frac{V_2}{T_2} \\ V_1\text{ is the first volume} \\ T_1\text{ is the first temperature} \\ V_2\text{ is the second volume} \\ T_2\text{ is the second temperature} \end{gathered}[/tex]Where
[tex]\begin{gathered} V_1=20.0\text{ L} \\ T_1=25\degree C \\ T_2=100\degree C \end{gathered}[/tex]Substitute the values of the variables into the Charles law formula
[tex]\begin{gathered} \frac{V_{1}}{T_{1}}=\frac{V_{2}}{T_{2}} \\ \frac{20.0}{25}=\frac{V_2}{100} \\ Crossmultiply\text{ } \\ V_2=\frac{100\times20.0}{25}=80.0\text{ L} \\ V_2=80.0\text{ L} \end{gathered}[/tex]Hence, the answer is 80.0 L