Aromatic compounds are compounds that contain carbon-carbon multiple bonds.
The question did not mention that a heteroatom is present in the compound so we can assume that there is none of such. In that case, the compound contains only hydrogen and carbon.
So,
(CH)n = 78
where n is the number of each atom present.
(12 +1)n = 78
n = 78/13
n = 6
The molecular formula of the compound is C6H6
When C6H6 is treated with .conc.HNO3/conc.H2SO4 the compound shown in image 1 is formed. The reaction occurs at the C-C multiple bond.
When C6H6 is reacted with chlorine in the presence of sunlight, hexachlorobenzene (shown in image 2 attached) is formed.
