An ideal gas undergoes four different processes from the same...

For adiabatic process,

$P ∝ \dfrac{1}{{V}^{\gamma}}$

For isothermal process,

$P ∝ \dfrac{1}{V}$

For isobaric process, $P =$constant

For isochoric process, $V =$constant

$∴$ Graphs for different processes

Adiabatic $⇒ 2$

Isothermal $⇒ 3$

Isobaric $⇒ 1$

$∴$The graph for adiabatic process is $2$.