An open flask has Helium gas at 2atm and 327°C. The flask is heated to 527°C at the same pressure. Th fraction of original gas remaining in the flask is

$\frac{P_1{V}_1}{ T_{1 }} =\frac{P_2{V}_2 }{T_{2 }}$

But the flask can hold only V1​ volume of air,

∴ Volume of air expelled=$\frac{V_1}{3}$

$Fraction of air expelled out= (V_1 / 3 )/(4V_1/3)$

$Fraction of air remaining in flask= 1-\frac{1}{4}=3/4$