Plant shoots exhibit positive phototropism by growing towards the light, while their roots exhibit negative phototropism by growing away from light. The hormone auxin directs this process. Auxin increases in concentration on the side of the shoots and the roots that faces away from the light. Auxin has different effects in each of these locations. What is the best explanation of how auxin directs phototropism in plant shoots?

Auxin increases in concentration on the side of the shoots and the roots that faces away from the light.

Explanation:

Auxin is a growth hormone in plants.it is promotes elongation of roots  and shoots. It is very sensitive to light. when the plant is exposed to light, the auxin in the  exposed part  of  the shoots breaks down. And diffuses to the shady part not exposed to light..

The higher concentration of auxin at this parts, promotes accelerated growth, which  caused the part to bend to of this shoot to grow faster than the other part, and bends towards light.

While the roots grows towards.

a covalent bond, specfically triple bond