An unknown gas 'X' is dissolved in water at 2.5 bar pressure and has mole fraction 0.04 in solution. The mole fraction of 'X' gas when the pressure of gas is doubled at the same temperature is :

Mole fraction of gas in the solution is proportional to the partial pressure of the gas.
Over the solution. $\mathrm{x}\propto \mathrm{P}$
$\frac{{\mathrm{x}}_1}{{\mathrm{P}}_1}=\frac{{\mathrm{x}}_2}{{\mathrm{P}}_2}$
Where, x1 = initial mole fraction of gas
P1 = Partial pressure of gas
x2 = Final mole fraction of gas
P2 = Final partial pressure of gas.
∵ Here only one gas
∴ Partial pressure of gas = Pressure of gas.
$\begin{array}{l}\frac{0.04}{2.5}=\frac{{\mathrm{x}}_2}{2\times (2.5)}\\ \Rightarrow {\mathrm{X}}_2=\frac{0.04\times 2\times 2.5}{2.5}\\ \Rightarrow {\mathrm{X}}_2=0.08\end{array}$