An ideal gas is expanded from $({\mathrm{p}}_1\mathrm{ },\mathrm{ }{\mathrm{V}}_1\mathrm{ },\mathrm{ }{\mathrm{T}}_1)\mathrm{ }\mathrm{to}\mathrm{ }({\mathrm{p}}_2\mathrm{ },\mathrm{ }{\mathrm{V}}_2\mathrm{ },\mathrm{ }{\mathrm{T}}_2)$ under different conditions. The correct statement(s) among the following is(are)

• Correct answer
  A

  The work done on the gas is maximum when it is compressed irreversibly from ( $p_2 , V_2)$ to $(p_1 , V_1)$ against constant pressure $p_1$
• Correct answer
  B

  If the expansion is carried out freely, it is simultaneously both isothermal as well as adiabatic
• Correct answer
  C

  The work done on 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.
• D

  The change in internal energy of the gas (i) zero, if it is expanded reversibly with $T_1= T_2$ , and (ii) positive, if it is expanded reversibly under adiabatic conditions with $T_1 \ne T_2$

Hence, the correct answer is options: 'A', 'B', 'C'.