A nucleoside comprises:

The correct answer is Option (3) → A nitrogenous base and a pentose sugar

Option (1) A nitrogenous base, a pentose sugar, and a phosphate group — Incorrect. All three together make a nucleotide. A phosphate added to a nucleoside turns it into a nucleotide.

Option (2) A nitrogenous base and a phosphate group — Incorrect. The base and the phosphate are never joined directly. Both are joined to the sugar: the base to its 1′ carbon and the phosphate to its 5′ carbon.

Option (3) A nitrogenous base and a pentose sugar — Correct. A base joined to a five-carbon sugar is a nucleoside, for example adenosine or deoxyadenosine.

Option (4) A pentose sugar and a phosphate group — Incorrect. Sugar and phosphate joined one after the other form the backbone of the polynucleotide chain. Without a base this is not a nucleoside.

NCERT Extract:
Structure of Polynucleotide Chain – …