
$\frac{{dP}}{{dV}} = - \gamma \frac{P}{V}$==> |Slope| $\propto \gamma$
From the given graph $(Slope)_2 > (Slope)_1$ ==> ${\gamma _2} > {\gamma _1}$
therefore $1$ should correspond to $O_2 (\gamma$ = 1.4) and $2$ should correspond to $He$ ($\gamma = 1.66$)





