Credit for the ring structure of benzene goes to

An aromatic compound of molecular formula $C_6H_4Br_2$ was nitrated,and three isomers of formula $C_6H_3Br_2NO_2$ were obtained. The original compound is:

Which of the following compounds is not aromatic?

The order of decreasing reactivity towards an electrophilic reagent,for the following compounds,is:
$(i) \text{ Benzene} \quad (ii) \text{ Toluene} \quad (iii) \text{ Chlorobenzene} \quad (iv) \text{ Phenol}$

The reagent used in Friedel-Crafts reaction is:

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