RNA is a labile molecule due to the presence of:

The correct answer is Option (4) → 2′-OH group

The carbons of the pentose sugar of a nucleotide are numbered 1′ to 5′. The two nucleic acids differ in their sugar: ribose in RNA has an -OH group at 2′, while deoxyribose in DNA has none there (“deoxy” means one oxygen less).

Option (1) 3′-OH group — Incorrect. The 3′-OH is present in both DNA and RNA. Two nucleotides are linked through a 3′-5′ phosphodiester bond, so this group builds the chain; it cannot explain why only RNA is unstable.

Option (2) 5′-OH group — Incorrect. The 5′ carbon is where the phosphate group is attached to form a nucleotide. It is common to DNA and RNA as well.

Option (3) 4′-OH group — Incorrect. The 4′ carbon is part of the sugar ring and carries no free -OH group in either nucleic acid.

Option (4) 2′-OH group — Correct. This reactive group is present only in RNA. It is one reason why DNA, and not RNA, is the better genetic material.

NCERT Extract:
Properties of Genetic Material (DNA Versus RNA) – “… The genetic material should be stable enough not to change with different stages of life cycle, age or with change in physiology of the organism. Stability as one of the properties of genetic material was very evident in Griffith’s ‘transforming principle’ itself that heat, which killed the bacteria, at least did not destroy some of the properties of genetic material. This now can easily be explained in light of the DNA that the two strands being complementary if separated by heating come together, when appropriate conditions are provided. Further, 2′-OH group present at every nucleotide in RNA is a reactive group and makes RNA labile and easily degradable. RNA is also now known to be catalytic, hence reactive. Therefore, DNA chemically is less reactive and structurally more stable when compared to RNA. Therefore, among the two nucleic acids, the DNA is a better genetic material.”