Which of the following represents $H$ückel's rule for aromaticity?

Identify the product $A$ in the following reaction:
$C_6H_6 + CH_2Cl_2 \xrightarrow{\text{Anhy. } AlCl_3} A$

Which of the following is/are produced when a mixture of benzene vapour and oxygen is passed over $V_2O_5$ catalyst at $775\, K$?

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

Number of $\pi$ electrons present in naphthalene is :