Correct option (b) isobaric
Explanation :
During expansion, work is performed by the gas. The isobaric expansion is represented by the horizontal straight line AB1. Since the adiabatic curve is steeper than the isothermal curve, the adiabatic expansion curve (AB3) must lie below the isothormal curve (AB2) as shown in the figure. Since area under AB1 is maximum, the work done is maximum in case of isobaric expansion.