Select an appropriate plant hormone responsible for apical dominance from the following.

$A$: If a plant is kept horizontally,auxin accumulates on the lower surface.
$R$: Displacement of statoliths and other cell organelles to the lower surface modifies the translocation pattern of auxin.

Give scientific reasons: Indole-$3$-acetic acid $(IAA)$ is not the only naturally occurring auxin.

Auxins inhibit the growth of

Plants with zinc deficiency show reduced biosynthesis of $..........$

If the growing coleoptile tip is cut,what happens to phototropism?