Step 1: Understanding the Concept:
Plant hormones are grouped by what raw material the plant builds them from. Auxins like IAA and IBA are built from the amino acid tryptophan. Gibberellins are built from a chain of terpene units. A separate small group is built by breaking down carotenoid pigments, the same orange-yellow pigments that colour carrots and autumn leaves.
Step 2: Key Approach:
To find the carotenoid-derived hormone in the list, check each option against its known building block rather than its function first.
Step 3: Detailed Explanation:
Indole-3-acetic acid and indole butyric acid both carry an "indole" ring in their name, a giveaway that they come from tryptophan, not carotenoids. Gibberellic acid is a diterpenoid, built from four terpene units joined together, again a different starting material. Abscisic acid, on the other hand, is made when an enzyme clips a 40-carbon carotenoid molecule (specifically a xanthophyll called violaxanthin) down into a smaller 15-carbon piece. That clipped piece is abscisic acid itself. Since only abscisic acid traces back to a carotenoid precursor, it is the one that fits the question.
Step 4: Final Answer:
Abscisic acid is the plant hormone built from a broken-down carotenoid, so option 4 is correct.