Three fused benzene rings are found in

According to $H$ückel's rule, a cyclic $\pi$-molecular orbital system must contain which of the following to be aromatic?

$A$ substance containing an equal number of primary,secondary and tertiary carbon atoms is:

Which of the following compounds will undergo electrophilic substitution more readily than benzene?

Arrange the following compounds in decreasing order of their reactivity towards electrophilic substitution $(E^{+})$:
$C_6H_5NH_2$,$C_6H_5NHCOCH_3$,$C_6H_6$,$C_6H_5SO_3H$

Which among the following is the strongest acid?