The presence of a nitro group in a benzene ring......

Identify the molecular formula of pyridine from the following.

The nitro group in nitrobenzene is a

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 reaction of benzene with $n$-propyl chloride in the presence of anhydrous $AlCl_3$ mainly yields ..........

All the hydrocarbons shown are very weak acids. One,however,is far more acidic than the others. Which one is the strongest acid?