Number of compounds among the following which contain sulphur as heteroatom is _______.
Furan, Thiophene, Pyridine, Pyrrole, Cysteine, Tyrosine

We need to count the number of compounds containing sulphur as a heteroatom from: Furan, Thiophene, Pyridine, Pyrrole, Cysteine, Tyrosine.

Define heteroatom.

A heteroatom is any atom in an organic compound that is not carbon or hydrogen. In heterocyclic chemistry, it specifically refers to atoms like N, O, S that replace carbon in a ring.

Analyse each compound.

Furan: A five-membered heterocyclic ring containing oxygen as the heteroatom. No sulphur.

Thiophene: A five-membered heterocyclic ring containing sulphur as the heteroatom. Counted.

Pyridine: A six-membered heterocyclic ring containing nitrogen as the heteroatom. No sulphur.

Pyrrole: A five-membered heterocyclic ring containing nitrogen as the heteroatom. No sulphur.

Cysteine: An amino acid with the structure $$HSCH_2CH(NH_2)COOH$$. It contains a thiol group ($$-SH$$), so sulphur is present as a heteroatom. Counted.

Tyrosine: An amino acid with a phenol group ($$HO-C_6H_4-CH_2CH(NH_2)COOH$$). It contains oxygen and nitrogen but no sulphur.

Count.

Compounds containing sulphur as heteroatom: Thiophene and Cysteine = 2.

The answer is 2.