The presence or absence of hydroxyl group on which carbon atom of sugar differentiates RNA and DNA?

Nucleic acids are made of repeating nucleotides. Each nucleotide consists of a pentose sugar, a nitrogenous base and a phosphate group.

1. In DNA the pentose sugar is 2-deoxyribose. In RNA the sugar is ribose.
2. The two sugars differ only at one carbon atom of the ring:

• Numbering of the pentose carbon atoms follows the convention $$1', 2', 3', 4', 5'$$ (or simply 1, 2, 3, 4, 5).
• In ribose (RNA) the $$2'$$ carbon carries an -OH (hydroxyl) group.
• In 2-deoxyribose (DNA) the $$2'$$ carbon lacks this -OH; it has -H instead.

Thus, the presence (in ribose) or absence (in deoxyribose) of the hydroxyl group on the $$2^{\mathrm{nd}}$$ carbon distinguishes RNA from DNA.

Option A which is: $$2^{\mathrm{nd}}$$