Nucleotides are formed by
a)	Purine, sugar and phosphate	b)	Purine, pyrimidine and phosphate
c)	Purine or pyrimidine, sugar and phosphate	d)	Pyrimidine, sugar and phosphate

(b)

The nucleotide is formed by the union of a phosphate group with a nucleoside. A nucleoside contains a sugar molecule along with an organic nitrogenous base. Thus, a nucleotide contains a organic nitrogenous base (purine or pyrimidine) along with a sugar molecule and a phosphate group,

Nucleoside=Sugar molecule+Organic nitrogenous base.

Nucleotide=Nucleoside+Phosphate group.