How many $\pi$ electrons are there in the following species:

In the following reaction,
$CH_3-C \equiv CH \xrightarrow[873 \ K]{\text{red hot iron tube}} A$
the number of sigma$(\sigma)$ bonds present in the product $A$ is

Give reason: Nitration of benzene is not possible with only $HNO_3$.

Which of the following is not an aromatic species?

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

Which of the following species participates in the sulphonation of the benzene ring?