Solution:
During night or dark: \(\mathrm{CO}_{2}\) conc. incresses in sub-stomatal cevities \(\rightarrow>\mathrm{ABA}\) participation \(\rightarrow \mathrm{K}^{+}\)ions exchange stopped \(\rightarrow \mathrm{K}^{+}\)ions transported back into subsidiary cells \(\rightarrow\) Decreased \(\mathrm{pH} \rightarrow>\) Starch synthesized in guard cells \(\rightarrow\) Decreased O.P of guard cells \(\rightarrow\) Exosmosis from guard cell \(\rightarrow\) Stomata close
