These two monomers have similar structures, but with a slight difference of sulphur atom replaced by a nitrogen atom bonded to hydrogen. Which pair represents these monomers?

Correct Answer: Thiophene and Pyrrole
Thiophene and Pyrrole have similar structures. Thiophene has a molecular formula of (C4H4S) while the molecular formula for Pyrrole is (C4H4NH). These molecules have alternating double and single bonds in their structures and hence they form pi-conjugated polymers.