Which of the following is not an external factor for plants?

Of the several gases in the atmosphere,plant life mostly depends upon

The concentration of $CO_2$ in the atmosphere is $...............$ and if the concentration of $CO_2$ is increased up to $\ldots \ldots \ldots$,it can lead to an increase in the rate of $CO_2$ fixation.

Blackman's law is concerned with

Who proposed the 'law of limiting factor' as the 'law of minimum'?

If a plant receives low-intensity light,then: