7. Following are certain statements regarding secondary metabolites found in plant:
   A. All terpenes are derived from a six carbon element.
   B. Alkaloids are nitrogen containing compounds.
   C. Pyrethroids, a monoterpene ester found in the leaves and flower of Chrysanthemum species, show insecticidal activity.
   D. Limonoids are groups of alkaloids and have anti­herbivoral activity.
   Which one of the following combinations of above statements is correct?
   (1) A and B            (2) A and D

(3) B and C           (4) C and D

Correct answer: (3) B and C

Explanation:

• (A) is incorrect:

  • Terpenes are derived from five-carbon isoprene units, not six-carbon elements.

• (B) is correct:

  • Alkaloids are nitrogen-containing secondary metabolites, often pharmacologically active.

• (C) is correct:

  • Pyrethroids, synthetic analogs of natural pyrethrins from Chrysanthemum species, are monoterpene esters with insecticidal activity.

• (D) is incorrect:

  • Limonoids are triterpenoid compounds, not alkaloids, and have anti-herbivorous activity.

Option-wise:

• (1) A and B — A false.

• (2) A and D — both false.

• (3) B and C — correct.

• (4) C and D — D false.

Alkaloids are nitrogenous secondary metabolites vital for plant defense and pharmacology; pyrethroids are monoterpene esters derived from Chrysanthemum with potent insecticidal properties, while limonoids are triterpenoids exhibiting anti-herbivory effects, demonstrating the biochemical variety in plant metabolites.