The excess amount of $CO_2$:

During $24$ hours,there is a specific time when plants neither release $O_2$ nor $CO_2$. This is the time of:

The optimum temperature for photosynthesis is ......... .

$C_{3}$-plants show optimum photosynthesis at

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

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.