Question

if we keep on increasing carbon dioxide concentration in air what will be the rate of photosynthesis

Answer 1

the rate of photosynthesis will increase because one of it's reactants has increased only if it is not limited by other factors(blackman's law of limiting factor)

Answer 2

as we know that carbon dioxide is present in the atmosphere in a very low concentration (about 0.04%) so because of the increase of carbon dioxide in the air rate of photosynthesis also increases