Question

Which of the following plant growth regulators is used as herbicide ?

• A. Gibberellin
• B. 2,4-D
• C. Kinetin
• D. Abscisic acid

Hint:

Keep this structural formula or shorthand in mind: 2,4-D = Dicot Destroyer. It kills Dicot weeds selectively. Because it is a synthetic auxin, it mimics normal plant hormones but acts like a poison at high concentrations only for broad-leaved plants, making it a stellar herbicide!

Answer 1

The Correct Option is B

Step 1: Understand the question.
We must find which plant growth regulator is used as a herbicide.
Step 2: Recall synthetic auxins.
Some synthetic auxins, at high doses, selectively kill certain weeds, and a classic example is 2,4-D.
Step 3: Explain 2,4-D action.
2,4-D kills broad-leaved dicot weeds while sparing narrow-leaved monocot crops, making it a selective herbicide. So 2,4-D is the answer.
Step 4: Reject gibberellin.
Gibberellin elongates stalks and improves fruit, but it never acts as a herbicide.
Step 5: Reject kinetin.
Kinetin is a cytokinin promoting cell division and delaying ageing, with no weed-killing role.
Step 6: Reject ABA and conclude.
Abscisic acid controls dormancy and stress, not weed killing. Therefore 2,4-D is the herbicide.
\[ \boxed{\text{2,4-D}} \]