An open vessel containing air is heated from 300K to 400K. The fraction of air which goes out of it of the originally present is?

As the vessel is open the pressure remains constant and there is no change in the volume of vessel. Hence volume also constant.According to ideal gas equationPV=nRTn1 =1 T1 =300k, T2=400 k n2=?P1V1=n1 RT1 , P2 V2=n2RTn1/n2 = T2/T11/n2 =400/300n2=3/4The fraction of air present in vessel after heating n2=3/4The fraction of air which goes out of the vessel =1-3/4=1/4