Who proposed the "Law of Limiting Factors"?

Light compensation point is the point where:

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

The rate of photosynthesis is maximum in the $P$ region of light and minimum in the $Q$ region of light.

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

The graph given below shows the effect of potassium cyanide on the rate of photosynthesis of Chlorella at different light intensities. Which one of the following can be deduced from the graph?