The reversible expansion of an ideal gas under adiabatic and...

$T_{1}=T_{2}$ because process is isothermal. Work done in adiabatic process is less than in isothermal process because area covered by isothermal curve is more than the area covered by the adiabatic curve. In adiabatic process expansion occurs byusing internal energy, hence, it decreases while in isothermal process temperature remains constant, that's why no change in internal energy.