Correct option is B
Explanation-
More than 130 types of gibberellins (GA₁ to GA₁₃₄+) have been identified.
Chemical Nature of Gibberellins:
Gibberellins are tetracyclic diterpenoid acids. They are synthesized from geranylgeranyl diphosphate (GGPP), which is a C₂₀ compound. GGPP itself is made by combining 4 isoprene (C₅) units.
So, 1 gibberellin molecule = 4 isoprene units = 20 carbon atoms (C₂₀).
Isopentenyl pyrophosphate (IPP) — the basic isoprene unit
IPP → GGPP (geranylgeranyl pyrophosphate) (C₂₀)
GGPP → ent-kaurene → oxidized to form various gibberellins (GA)
This confirms their classification as diterpenoids, because they originate from a C₂₀ precursor.
Incorrect options -
Option A - Monoterpenes (C₁₀): Too small — only 2 isoprene units. (e.g., limonene)
Option C - Triterpenes (C₃₀): Too large — 6 isoprene units. (e.g., precursors to steroids)
Option D - Sesquiterpenes (C₁₅): 3 isoprene units — not related to gibberellins.
So, the correct answer is option B - Diterpenes (C₂₀)
