At T=300K, V=1litre
Let on heating the gas ,new volume of gas becomes V at T=310k
Therefore at constant pressure
V_1T_1=V_2T_2
1300=\frac { V }{ 310 }
V=1.0333litre
Since capacity of flask is one litre , therefore gas escaped out from the flask is 1-0.333litre=0.0333litre-33.3mL