The question asks which plot is incorrect for a diatomic ideal gas in a closed system, but the actual graphs/options A, B, C, D are missing from the prompt.

So, the key issue is:

1. The question depends entirely on the shapes/labels of the plots.
2. Since those plots are not visible or described, it is impossible to evaluate which one is incorrect.
3. Therefore, no valid derivation of the correct option can be made from the information provided.

What would normally be used for such a question?

For a diatomic ideal gas (assuming no vibrational modes active), we use:

$C_V = \frac{5}{2}R, \qquad C_P = \frac{7}{2}R$

and for an ideal gas,

$U = nC_V T, \qquad H = nC_P T$

Also,

$PV = nRT$

So common valid graph relations are:

1. $U \propto T$
2. $H \propto T$
3. $PV \propto T$
4. At constant volume, $P \propto T$
5. At constant pressure, $V \propto T$
6. $H-U = nRT$

But without the actual plotted axes and curve shapes for options A–D, we cannot determine which plot is wrong.

Conclusion

The problem statement is incomplete because the plots are missing. Hence the answer cannot be verified from the supplied data.