P-V plots for two gases during adiabatic processes are shown in the figure. Plots 1 and 2 should corresponds respectively to

Explanation

In adiabatic process
Slope of P-V graph, `(dP)/(dV)=-gamma(P)/(V)`
Slope `prop gamma` (with negative sign)
From the given graph, (slope)`_(2)gt`(slope)`_(1)`
`therefore gamma_(2)gtgamma_(1)`
Therefore, '1' should correspond to `O_(2)(gamma=1.4)`
and '2' should correspond to `He(gamma=1.67)`.