Which of the following compounds or ions is not aromatic?

Give the decreasing order of reactivity for the $ESR$ (Electrophilic Substitution Reaction) for the following compounds:
$(1)$ Benzene
$(2)$ Toluene
$(3)$ Chlorobenzene
$(4)$ Nitrobenzene

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:
$CH_3CH_2CH_2CH_2Br$ $\xrightarrow[\text{dry ether}]{Na} X$ $\xrightarrow[\text{10-20 atm}]{\text{Cr}_2\text{O}_3 / 773 \text{ K}} Y$ $\xrightarrow[\text{anhy. AlCl}_3]{\text{CH}_3\text{COCl}} Z$

What is meant by activating groups? Explain with suitable examples.

Deduce the structure of $(A)$.
$(A) \ C_{8}H_{10}$ $\xrightarrow{KMnO_{4}} (B) \ C_{8}H_{6}O_{4}$ $\xrightarrow[Fe]{Br_{2}} C_{8}H_{5}BrO_{4} (C)$ (one-product only)

Among the following,the number of aromatic compound$(s)$ is