What is formed by the nitration of nitrobenzene in the presence of fuming nitric acid?

The electrophile $NO_2^+$ reacts with which of the following compounds? In which case will $NO_2^+$ attack at the meta position?
$(I)$ $C_6H_5-CCl_3$
$(II)$ $C_6H_5-NO_2$
$(III)$ $C_6H_5-CHO$
$(IV)$ $C_6H_5-O^-$

Arrange the following in increasing order of rate of Nitration:
$(a)$ Benzene
$(b)$ Toluene
$(c)$ Hexadeuterobenzene $(C_6D_6)$
$(d)$ Nitrobenzene
$(e)$ Chlorobenzene

Among the following,the total number of meta-directing functional groups is $ . . . . . . $ (Integer based).
$-OCH_3, -NO_2, -CN, -CH_3, -NHCOCH_3, -COR, -OH, -COOH, -Cl$

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.

Discuss the formation of cancer-causing polynuclear hydrocarbons and explain how they cause cancer.