The combination of plots which does not represent isothermal expansion of an ideal gas is:

The correct option is A B and D
For an isothermal expansion,
$P{V}_m=kso,P=k/V_m$
where k is a constant.

graph A :
So here it means $P$ is directly proportional to $1/V_m$ i.e
$P\propto \frac{1}{V_m}$, so graph A is correct.

graph B:
Since $P\propto \frac{1}{V_m}$ so graph of $Pvs{V}_m$ should be parabolic in nature but it is given as a straight line so it is not correct.

graph C:
For isothermal expansion,
$P{V}_m=$ constant
graph C is also correct.

graph D:
As U is constant for an isothermal ideal gas expansion, hence graph D is incorrect

So incorrect graphs are B and D.

The correct graphs for B and D are given below.