Answer
Isobaric process.
Work Step by Step
For the isobaric expansion:
$W = \int PdV$
$W = P_0(V_f-V_0)$
For the isothermal expansion:
From Boyle's Law:
$PV = k = P_0V_0$
$W = \int \frac{k}{V}dV$
$W = P_0V_0\ \ln(\frac{V_f}{V_0})$
The equations display what can be observed in the P-V diagram: the work done in an isothermal process is the area under an isothermal curve and the work done in an isobaric process is the area of the rectangle surrounding the isothermal curve entirely, therefore, the work done in an isobaric process will always be greater in magnitude than in an isothermal process.
