1. 2 dm³
2. 3 dm³
3. 4 dm³
4. 8 dm³

Solution: 4 dm³

From ideal gas equation, we have:

$ \frac{{{P}_{1}}{{V}_{1}}}{{{T}_{1}}}=\frac{{{P}_{2}}{{V}_{2}}}{{{T}_{2}}} $

$ We\,have\,: $

$ {{P}_{1}}=P,\,{{T}_{1}}=T,\,{{V}_{1}}=V\,\,and\,\,{{P}_{2}}=2P,\,{{T}_{2}}=2T $

$ \therefore {{V}_{2}}={{V}_{1}}=V\, $

and, V = 4 dm³

The volume remains unchanged.