Which is the most important limiting factor in normal conditions for photosynthesis?

Assertion : The atmospheric concentration of $CO_2$ at which photosynthesis just compensates for respiration is referred to as $CO_2$ compensation point.
Reason : The $CO_2$ compensation point is reached when the amount of $CO_2$ uptake is less than that generated through respiration because the level of $CO_2$ in the atmosphere is more than that required for achieving $CO_2$ compensation point.

Write the effect of concentration of $CO_2$ on $C_3$ and $C_4$ plants.

One of the effects of dust is to cause

If a plant is provided with optimal temperature,light,and $CO_2$ for photosynthesis,but water is supplied in limited amounts,the rate of photosynthesis will follow which of the following factors?

Which of the following statements is $NOT$ consistent regarding the factors affecting the rate of photosynthesis?