What is the decreasing order of reactivity amongst the following compounds towards aromatic electrophilic substitution?
$I.$ Chlorobenzene
$II.$ Benzene
$III.$ Anilinium chloride
$IV.$ Toluene

The reaction of benzene with isobutylene in the presence of $H_2SO_4$ gives:

Nitrobenzene can be prepared from benzene by using a mixture of conc. $HNO_3$ and conc. $H_2SO_4$. In the mixture,nitric acid acts as a/an

Which of the following compounds is not aromatic?

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

Rank the following compounds in order of increasing rate of reaction towards Electrophilic Aromatic Substitution $(EAS)$ with bromine in the presence of $FeBr_3$.