Please solve question no.4.

Dear Student,

The correct logical sequence is 

Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen
The energy in the form of photons is absorbed by the Grana, with the help of pigment chlorophyll and the absorbed energy further splits water molecules in hydrogen and hydroxyl ions whereas stoma(stomata) takes in carbon dioxide to release oxygen.
Sequence of above events is:
1. The chlorophyll on exposure to light energy becomes activated by absorbing photons.
2. This energy is used in splitting water molecules.
    H₂O $\underset{}{\overset{Photolysis of water}{\to }}$ H⁺  +    OH-
3. OH^- through series of steps produce oxygen which is used by organisms.

Regards