​During the most common form of protein glycosylation in the ER, a preformed precursor oligosaccharide which is transferred as a complete unit to the asparagine residue in a protein is:​

Correct option is B

The correct answer is (b).
In the N-linked glycosylation pathway, the oligosaccharide Glc3Man9GlcNAc2 (containing 2 N-acetylglucosamines, 9 mannoses, and 3 glucoses) is transferred from a lipid carrier (dolichol pyrophosphate) to a nascent protein's asparagine residue in the lumen of the ER. The sugar residues involved are added sequentially, and the structure described in option (b) is the one that is most commonly transferred during this process.
Incorrect options-
Option (a): Incorrect because it states 3 N-acetylglucosamines and 10 mannoses and 4 glucoses, which does not match the known oligosaccharide structure; the number of N-acetylglucosamines is always 2.
Option (c): Incorrect as the oligosaccharide contains 2, not 3, N-acetylglucosamines.
Option (d): Incorrect as it undercounts mannose residues (8 instead of 9). This incomplete structure is not the precursor transferred during glycosylation.