Conversion of IBA to IAA occurs via β‑oxidation in:
Pick C: Peroxisomes. Thinking through Phytohormone ALL step by step rules out the lookalikes and leaves Peroxisomes. Skip these: A) Mitochondria; B) Plastids; D) Cytosol. For hormones and genes, match the molecule or gene to its real role, not a neighboring pathway.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.