A stomata closes when : (i) it needs carbon dioxide for photosynthesis. (ii) it does not need carbon dioxide for photosynthesis. (iii) water flows out of the guard cells. (iv) water flows into the guard cells. The correct reason(s) in this process is/are :

Stomata are pores used for gas exchange. The opening and closing of these pores are regulated by guard cells.

• Reason (ii): Plants close stomata when they do not require $CO_2$ for photosynthesis (often at night or during water stress) to prevent unnecessary water loss. The NCERT text mentions the photosynthesis reaction: $6CO_2(aq) + 12H_2O(l) \xrightarrow{Sunlight} C_6H_{12}O_6(aq) + 6O_2(aq) + 6H_2O(l)$.
• Reason (iii): The closing occurs when water flows out of the guard cells, causing them to shrink and become flaccid, which pulls the pore shut.
• Distractors (i) and (iv): These describe the conditions for stomatal opening (needing $CO_2$ and water flowing into guard cells to make them turgid).