a. To balance the given reaction
Let us write the balanced equation as
By inspection, balancing
Next let us balance
Now left is only
if we observe closely we see that number
We know that the reaction represents the process of photosynthesis which takes place in plants, some algae and cyanobacteria.
Sometimes the reaction of photosynthesis is written as
b. Like other endothermic reactions, photosynthesis does not absorb energy in the form of heat, therm is unit of heat. But there would no reaction in the absence of light energy.
In other words energy in the form of sunlight needs to be made available in order that photosynthesis reaction occurs. As such it should be called an endothermic reaction, though not in strict sense.
c. The sunlight energy is converted in to chemical energy which is stored in the form of glucose molecules.