The plant hormone used to destroy weeds in a field is :

The correct option is 2, 4-D.

Step-by-step Explanation:

1. What is 2, 4-D?
2, 4-D (2, 4-Dichlorophenoxyacetic acid) is a synthetic auxin, which is a class of plant hormones responsible for regulating plant growth and development.

2. How does it act as a weedkiller?
When applied in higher concentrations, 2, 4-D behaves as a highly selective herbicide. It specifically targets and destroys broad-leaved (dicotyledonous) weeds by causing rapid, uncontrolled growth that leads to their death. Crucially, it does not harm narrow-leaved (monocotyledonous) crop plants, making it ideal for weed control in fields of cereals like wheat, rice, and corn.

3. Why are the other options incorrect?
- IAA (Indole-3-acetic acid): This is a naturally occurring plant auxin primarily responsible for cell elongation, apical dominance, and general growth regulation, rather than weed eradication.
- IBA (Indole-3-butyric acid): This is another plant hormone commonly used in gardening and agriculture to promote root formation in stem cuttings.
- NAA (Naphthalene acetic acid): This is a synthetic auxin used to induce flowering and prevent the premature shedding of leaves and fruits, but it is not typically used as a weedkiller.