The correct answer is A. Blue.
Photosynthesis is the process by which plants use sunlight to convert carbon dioxide and water into oxygen and energy in the form of sugar. Chlorophyll, a green pigment found in chloroplasts, absorbs sunlight and uses the energy to split water molecules into hydrogen ions and oxygen gas. The hydrogen ions are then used to create ATP, a molecule that stores energy. The oxygen gas is released into the atmosphere.
The different wavelengths of light have different energies. Blue light has the shortest wavelength and the highest energy, while red light has the longest wavelength and the lowest energy. Chlorophyll absorbs blue light most efficiently, followed by red light. Green light is reflected by chlorophyll, which is why leaves appear green.
The other options are incorrect because they are not absorbed by chlorophyll as efficiently as blue light.