$A$ linear relationship exists between incident light and the rate of $CO_2$ fixation at/in:

Photosynthetic rate and productivity will increase by increasing $CO_2$ concentration in :-

$A-$ The $C_3$ and $C_4$ plants respond differently to $CO_2$ concentrations.
$R -$ The concentration of $CO_2$ in the atmosphere is between $0.03$ and $0.04$ percent. An increase in concentration up to $0.05$ percent can cause an increase in $CO_2$ fixation rates.

The figure shows the effect of light on the rate of photosynthesis. Based on the graph,answer the following questions:
$(a)$ In which region/s (indicated by arrows) is light a limiting factor?
$(b)$ What could be the limiting factor/s in the region where the rate of photosynthesis becomes constant?
$(c)$ What does the point where the curve flattens represent?

Which of the following statements is incorrect?

In an experiment demonstrating the evolution of oxygen in $Hydrilla$,sodium bicarbonate is added to water in the experimental set-up. What would happen if all other conditions are favourable?