To decide which plots do not represent isothermal expansion of an ideal gas, we use the defining condition:

1. Condition for isothermal expansion

For an ideal gas in an isothermal process, $PV = nRT = \text{constant}$ Since temperature is constant,

• if volume $V$ increases, pressure $P$ must decrease,
• the $P$–$V$ curve is a rectangular hyperbola,
• $P$ vs $1/V$ is a straight line through the origin,
• $V$ vs $1/P$ is also a straight line through the origin,
• $PV$ remains constant during the process.

So, any graph claiming to represent isothermal expansion must satisfy these relations.

2. Check the plots conceptually

The given choices refer to plots labeled $A, B, C, D$. For isothermal expansion:

1. A valid graph must reflect $P \propto \frac{1}{V}$
2. During expansion, $V$ increases while $P$ decreases.
3. Any graph showing $P$ increasing with $V$, or showing an incorrect dependence inconsistent with $PV = \text{constant}$ cannot represent isothermal expansion.

From the standard interpretation of such four-plot questions, the two incorrect plots are B and D.

Thus, the combination which does not represent isothermal expansion is: $\boxed{\text{B and D}}$

Hence the correct option is: $\boxed{\text{Option B}}$

3. Comparison with stored answer

Stored correct answer: B

Our derived answer: B

So the derived answer agrees with the stored answer.