Concept:The light reaction stage uses sunlight to produce energy carriers, while carbon dioxide fixation happens in the dark stage.
Explanation:In the light reaction, chlorophyll absorbs sunlight and becomes energised.
This light energy splits water molecules through photolysis:
H2O→H++OH−.
The hydroxyl ions
OH− produced are a key intermediate of this splitting.
These hydroxyl ions later release electrons and form oxygen:
4OH−→2H2O+O2+4e−.
The electrons are transferred along the electron transport chain to generate ATP and NADPH.
However, Carbon (IV) oxide combining with hydrogen is not a light reaction event.
This combination represents carbon dioxide fixation, which occurs later in the dark stage (Calvin cycle) inside the stroma.
The hydrogen used there is supplied by NADPH produced during the light stage.
Thus, among the listed events, only option B does not occur in the light reaction.
Answer:The event that does not occur in the light reaction stage is Carbon (IV) oxide combining with hydrogen.
Correct option: B.