Which of the following is not an example of a benzenoid compound?

Given the following structures:
$(I)$ $1,3,5-$trimethylbenzene (mesitylene)
$(II)$ $1,3-$dimethyl$-5-$methylenecyclohexa$-1,3-$diene
$(III)$ $1,3,5-$trimethylenecyclohexane
The enthalpy of hydrogenation of these compounds will be in the order as:

What is the major product of the following reaction?

The $C - C$ bond length in benzene is ...... $\mathring{A}$.

When acetylene is passed through a red hot iron tube,compound $X$ is formed. Which one of the following reactions will yield $X$ as the major product?

Which of these will produce the highest yield in a Friedel-Crafts reaction?