Benzene reacts with fuming sulphuric acid and give benzene sulphonic acid. Although S03 molecule it does not have positive charge, yet it is a strong electrophile. This is because the octet of electrons around the sulphur atom is not reacted. This reached is reversible and desulphonation occus readily in aqueous medium.

Coal tar is a viscous liquid obtained by the pyrolysis of coal. During fractional distillation, coal tar is heated and distills away its volatile compounds, namely, benzene, toluene, xylene in the temperature range of 350 K to 443 K. These vapours are collected at the upper part of the fractionating column.

(i) Each carbon atom in benzene possess an unhybridised p-orbital containing one electron. The lateral overlap of their p-orbitals produces 3n-bond, six electrons of the p-orbitals over all the six carbon atoms and are said to be delocalised.
(ii) Due to delocalisation, strong rt-bond is formed which makes the molecule stable. Hence unlike alkenes and alkynes, benzene undergoes substitution reactions rather than addition reactions under normal conditions

Kekule suggested that benzene consists of a cyclic planar structure of six carbon with alternate single and double bonds.
There were two objections:
(i) Benzene forms only one ortho disubstituted products whereas the Kekule's structure predicts two ortho disubstituted products as shown:

(ii) Kekule's structure failed to explain why benzene with three double bonds did not give addition reaction like alkenes.
To overcome this objection, Kekule suggested that benzene was a resonance hybrid of two forms(l and 2) which are in rapid equilibrium.

Alkyne undergoes two types of potymerisation reaction
(i) Linear polymerisation: Acetylene forms linear polymer, when passed into a solution of cuprous chloride and ammonium chloride
\(2CH\equiv CH\overset { { Cu }_{ 2 }{ Cl }_{ 2 } }{ \underset { { NH }_{ 4 }Cl }{ \longrightarrow } } \underset { (vinyl\quad acetylene) }{ { { CH }_{ 2 } }=\underset { \overset { | }{ C\equiv CH } }{ CH } } \) 
(ii) Cyclic polymerisation:  Acetylene undergoes cyclic polymerisation on passing through red hot iron tube. Three molecules of acetylene polymerises to form benzene.