Let us consider that the gas is ideal gas.Here, pressure is constant .Volume is constant as volume of gas is actually volume of container which is not changing , gas is just escaping out .So , no. of molecules changes if initially there were n molecules now 1/3 escape out so we are left with 2/3 molecules .Hence , no. of molecules =2/3 nUsing , ideal gas equation we have ,PV=nRTfrom this eq we get that T is inversely proportional to n ( no. of molecules)Hence , T1/T2=n2/n1T1=27u00b0C=273+27=300Kn2=(2/3)*n1Put these values in the above eq we get 300/T2=n1/(2/3)*n1Thus, T2=(300*3)/2 =450K =177u00b0C