Step 1: Know the basic nucleic acid building blocks.
DNA and RNA are made of nucleotides. It is important to distinguish between a nucleoside and a nucleotide.
Step 2: Define nucleoside.
A nucleoside = nitrogenous base + sugar (ribose in RNA, deoxyribose in DNA). Examples: adenosine, guanosine, cytidine, thymidine.
Step 3: Define nucleotide.
A nucleotide = nitrogenous base + sugar + one or more phosphate groups. So a nucleotide is a nucleoside plus phosphate.
Step 4: Why are the other options wrong?
Option 1 includes a phosphate group, which describes a nucleotide, not a nucleoside. Option 3 has no sugar, which is not a known biomolecule in this context. Option 4 uses 'non-nitrogen base', which does not exist in nucleic acid chemistry.
Step 5: Conclude.
A nucleoside contains only the nitrogenous base linked to a sugar moiety. No phosphate group is present.
Answer: Option (2) — Nitrogen Base + Sugar Moiety only