What is the phenomenon that is causing the bean seedling to bend as shown? O gravitropism
O phototropism
O rapid response
O thigmotropism

The answer is B. phototropism.

Phototropism is the orientation of a plant or other organism in response to light, either toward the source of light ( positive phototropism ) or away from it ( negative phototropism ).

So as we can see here the seedling is bending towards the sunlight, which is positive phototropism

If the experiment was perfomed more then once and you get the same results

The answer is lymph sinuses.