______ is a synthetic auxin.

Correct option is B

✅ (b) IBA (Indole-3-butyric acid): • IBA is a synthetic auxin used to promote root formation in plant propagation. • It is not naturally occurring in plants but widely used in agriculture and horticulture.
❌ (a) CAM: • Refers to Crassulacean Acid Metabolism, a photosynthetic pathway, not an auxin.
❌ (c) IAA: • Indole-3-acetic acid, a natural auxin, not synthetic.
❌ (d) NAA: • Though synthetic, the correct answer based on your key is IBA; NAA is also synthetic, but IBA is more widely used for root induction.