Concept:
At constant temperature, Boyle’s law is used:
\[
P_1V_1 = P_2V_2
\]
Step 1: Write the given values.
\[
V_1 = 4.2~dm^3
\]
\[
P_1 = 101~kPa
\]
\[
P_2 = 235~kPa
\]
\[
V_2 = ?
\]
Step 2: Apply Boyle’s law.
\[
P_1V_1 = P_2V_2
\]
\[
(101)(4.2) = (235)V_2
\]
\[
V_2 = \frac{101 \times 4.2}{235}
\]
\[
V_2 = \frac{424.2}{235}
\]
\[
V_2 \approx 1.8~dm^3
\]
Step 3: Conclusion.
Hence, the required volume is:
\[
\boxed{1.8~dm^3}
\]