The correct answer is c) abscisic acid. Abscisic acid is the plant hormone that triggers the fall of mature leaves and fruits, a process known as abscission.
Explanation:
Abscisic acid (ABA) is a growth inhibitor in plants. It plays a key role in abscission, promoting the formation of an abscission layer at the base of leaves, fruits, and other plant parts, leading to their shedding.
Why other options are incorrect:
a) Auxin:
Auxin promotes cell elongation and growth, and it helps prevent premature fruit and leaf drop in early stages.
b) Gibberellin:
Gibberellins promote stem elongation and growth, but they don’t directly trigger abscission.
d) Cytokinin:
Cytokinins stimulate cell division and growth, and they also have a role in delaying leaf senescence, which is the aging and eventual falling of leaves.