Which statement is correct for photosynthesis?

Blackman demonstrated that increasing illumination increased the photosynthetic rate up to a point when $CO_2$ becomes limiting. If light was not limiting,temperature becomes limiting. Emerson found that maximum $CO_2$ fixation could be achieved with brief flashes of light. Mark the correct statement in the following:

Which of the following statements is correct regarding $C_4$ plants?

In which of the following is light energy stored in the form of chemical energy?

Provide the differences between:
$(1)$ Light reaction (Light phase) and Dark reaction (Biosynthetic phase)
$(2)$ Mesophyll cells and Bundle sheath cells

What is the unique process which has supported life on this planet?