Which compound contains delocalized electrons?

Which of the following statements are correct?
$I$. In nitrating mixture,nitric acid participates as an acid.
$II$. $\sigma$-complex is the intermediate substance in electrophilic substitution of benzene.
$III$. Benzene on Friedel-Crafts alkylation with $n$-propyl chloride gives isopropyl benzene.

The reaction $C_6H_6 \rightarrow C_6H_5CH_3$ is known as:

Assertion : Benzene removes a butter stain from a table cloth.
Reason : Butter has an affinity towards benzene.

$C_6H_5-CH_3$ $\xrightarrow{KMnO_4} A$ $\xrightarrow[\Delta]{NaOH + CaO} B$, product $B$ is

Suitable conditions to prepare hexachlorobenzene $(C_6Cl_6)$ from benzene $(C_6H_6)$ is/are: