What is the number of $\pi$ bonds in naphthalene?

When a mixture of concentrated $HNO_3$ and $H_2SO_4$ reacts with benzene at $353 \, K$,what is the name of this reaction?

Which one of the following methods is suitable to generate aromatic compound$(s)$ from linear aliphatic saturated hydrocarbons with at least six carbon atoms?

Friedel-Crafts acylation is

Identify the product $X$ obtained in the following reaction:
$CH_{3}-(CH_{2})_{4}-CH_{3} \xrightarrow{Cr_{2}O_{3}, 773 \ K, 10-20 \ atm} X$

Which active species is involved in the nitration of benzene with concentrated nitric acid and concentrated sulfuric acid?