For isothermal process \(T\) is constant

So \(\Delta U =0\)

\(A \longrightarrow II\)

Adiabatic process

\(\Delta Q =0\)

\(\Delta Q =\Delta U +\Delta W\)

\(\quad \Delta U =-\Delta W\)

Work done by gas is positive

So \(\Delta U\) is negative

\(B \longrightarrow I\)

For Isochoric process \(\Delta W =0\)

\(C \longrightarrow IV\)

For Isobaric process

\(\Delta W = P \Delta V \neq 0\)

\(\Delta U = nC _{ V } \Delta T \neq 0\)

Heat absorbed goes partly to increase internal energy and partly do work.