Question

Among the following compounds how many is(are)unstable at room temperature in their pure form?

Answer 1

Only antiaromatic compounds having $4{\pi }^n$ electron where $n=1,2,3,....$ and all carbon have $s{p}^2$ centre are unstable.

So, $\left(b\right),\left(c\right),\left(h\right)$ are unstable.