The best answer is “It converts light energy to chemical energy”.
Photosynthesis fulfills many functions as those described in the other options, however the primary function is to perform a chemical reaction that needs the energy provided by sunlight and captured by the chlorophyll found in the green leaves of plants, to combine water molecules obtained by the roots and conducted by the stem to the leaves, in turn bringing mineral salts from the soil, the carbon dioxide molecules obtained by the respiration of the plants; and obtain as a result chemical energy in the form of glucose (simple vegetable sugar) that is stored for use in different functions of plant growth.
In the chemical process of photosynthesis, oxygen molecules are released, carbon dioxide is absorbed, energy is converted into mass, etc., but the central purpose of photosynthesis is to take advantage of the light energy provided by the sun, to transform the carbon and oxygen contributed by the carbon dioxide gas and the hydrogen and oxygen molecules contributed by the water in chemical energy to be stored and then used by the plant for its growth.
