When algae is exposed to sunlight, blue and red wavelengths of light are absorbed by the algae to produce sugars. energy from green wavelengths is not absorbed. how does this phenomenon validate the law of conservation of energy?
green wavelengths are reflected from the algae.
green wavelengths do not contain any energy.
the algae are a closed system, so unused energy is allowed to exit the system.
the law of conservation of energy applies to physical, not biological, systems.

The correct answer would be Green wavelengths are reflected from the algae.

The law of conservation states that the total energy of a closed system remains the same. In simple words, energy is neither created nor it can be destroyed but it can change from one form to another.

Similarly, in photosynthetic organisms such as algae, green light is reflected in the surrounding due to they appear green in color.  

The absorbed light (red and blue wavelengths) are converted into chemical energy (food) through photosynthesis.

It ensures that the total energy of the system remains the same and thus, the law of conservation of energy is not violated.