An open vessel at 27° C is heated until three fourths mass of the air in it has been expelled. Neglecting the expansion of the vessel, the temperature to which the vessel has been heated is 

Given data: 

Open vessel Temperature=27+273=300 K

Mass =¾ times expelled 

mass of gas at 273 K be n=$n_1$

​∴ moles of air left at T=$\mathrm{n}-\frac{3}{4}\mathrm{n}=\frac{\mathrm{n}}{4}$

Same condition of pressure and volume then

${\mathrm{n}}_1{\mathrm{T}}_1={\mathrm{n}}_2{\mathrm{T}}_2$

$\begin{array}{c}\mathrm{n}\times 300=\frac{\mathrm{n}}{4}\times \mathrm{T}\end{array}$

T=1200 K=926.85° C

Therefore the required option is A.