Gas at a pressure P_{o i}s contained in a vessel. If the masses of all the molecules are halved and their speeds are doubled, the resulting pressure P will be equal to : 

2 P_o

\(P = \frac{1}{2} \frac{mN}{V}v^2_{rms}\)

\(\Rightarrow P \propto mv^2_{rms}\)

\(\frac{P_2}{P_1} = \frac{m_2}{m_1} (\frac{v_2}{v_1})^2\)

\(\frac{P_2}{P_1} = \frac{m_1/2}{m_1} (\frac{2v_1}{v_1})^2\) = 2

\(P_2 = 2P_1 = 2P_o\)