The correct option is C (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
(a) Fruit ripener – Ethephon
Ethephon is the most widely used commercial source of ethylene. It hastens fruit ripening.
(b) Herbicide - 2, 4-D
2, 4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin widely used as herbicide. Herbicides are chemicals that kill or inhibit the growth of unwanted plants such as weeds. 2, 4-D kills dicotyledonous weeds.
(c) Bolting agent - (GA3)
Gibberellic acid (GA3) promotes bolting (internode elongation just prior to flowering) and this helps the elongation of the plants.
(d) Stress hormone - Abscisic acid (ABA)
ABA is derived from carotenoids. It helps plants to overcome situations of stress and is thus known as stress hormone.