Maximum work that could be secured by expanding the gas over a given pressure range is the __________ work.

Answer: Option A

The isentropic process is nothing but reversible adiabatic process since between the isothermal and adiabatic process the isothermal process has maximum area under $$P-V$$  diagram the isothermal process will have maximum work done during expansion. Since the slope of $$p-v$$   plot for adiabatic process is greater than isothermal process.