An ideal gas is expanded from $\left(p_1, V_1, T_1\right)$ to $\left(p_2, V_2, T_2\right)$ under different conditions. The correct statement(s) among the following is(are)
[$A$] The work done on the gas is maximum when it is compressed irreversibly from ( $\mathrm{p}_2, \mathrm{~V}_2$ ) to ( $\mathrm{p}_1, \mathrm{~V}_1$ ) against constant pressure $\mathrm{pl}_1$
[$B$] The work done by the gas is less when it is expanded reversibly from $V_1$ to $V_2$ under adiabatic conditions as compared to that when expanded reversibly from $V_1$ to $V_2$ under isothermal conditions
[$C$] The change in internal energy of the gas is ($i$) zero, if it is expanded reversibly with $T_1=T_2$, and ($ii$) positive, if it is expanded reversibly under adiabatic conditions with $T_1 \neq T_2$
[$D$] If the expansion is carried out freely, it is simultaneously both isothermal as well as adiabatic
