Why blue light elicits a positive phototropic?

Phototropism is the growth of an organism which responds to a light stimulus. It is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light.

The correct answer is  "c".  it is "c" because melting is an endothermic change, and endothermic get's energy from surroundings.