Growth promoting substance in plant is:

Explanation

The correct answer is I.A.A (Indole-3-acetic acid), which is an auxin, a class of plant hormones that are essential for cell elongation, root development, and various other growth processes. Auxins like I.A.A are key in regulating plant growth and encouraging developmental changes.F.A.D is unrelated to growth promotion because it functions primarily in energy transfer and redox reactions. Chlorophyll a is essential for photosynthesis, converting light energy into chemical energy, but it is not a hormone involved in growth promotion. ABA, while important for stress response and dormancy, acts more as a growth inhibitor rather than a promoter.