Which of the following compounds is used for the laboratory preparation of benzene?

The correct order of reactivity towards electrophilic substitution reaction is:

The number of $\pi$ electrons in the following molecule is:

What is the molecular formula of the product formed when benzene is reacted with ethyl chloride in the presence of anhydrous aluminium chloride?

Consider the following sequence of reactions. In $Z$,the number of $sp^3$ carbons is $a$ and $sp^2$ carbons is $b$. The value of $(a+b)$ is:
$CH_3CH_2CH_2CH_2Br$ $\xrightarrow[\text{dry ether}]{Na} X$ $\xrightarrow[\text{10-20 atm}]{\text{Cr}_2\text{O}_3 / 773 \text{ K}} Y$ $\xrightarrow[\text{anhy. AlCl}_3]{\text{CH}_3\text{COCl}} Z$

The product obtained in the reaction of benzene with chlorine in the presence of ultraviolet light is ...... .