(c) For Isothermal process $PV =$ constant
$\Rightarrow \left( \frac{dP}{dV} \right) = \frac{- P}{V} =$ Slope of Isothermal curve
For adiabatic $PV^{\gamma} =$ constant
$\Rightarrow \frac{dP}{dV} = \frac{- \gamma P}{V} =$ Slope of adiabatic curve
Clearly, $\left( \frac{dP}{dV} \right)_{adibatic} = \gamma\left( \frac{dP}{dV} \right)_{Isothermal}$