$2 H_{2} O \rightarrow 4 H^{+} + O_{2} + 4 e^{-}$
Based on the above equation,answer the following questions:
$(a)$ Where does this reaction take place in plants?
$(b)$ What is the significance of this reaction?

(N/A) This reaction takes place in $PS-II$,which is located on the inner side of the thylakoid membrane. It is the site of water splitting (photolysis of water),where electrons are released from water molecules. Ions like $Mn^{2+}$ and $Cl^{-}$ act as essential cofactors for this process.
$(b)$ The significance of water splitting in photosynthesis is as follows:
$(i)$ $O_{2}$ is released as a byproduct,which is the primary source of atmospheric oxygen essential for the survival of aerobic organisms.
$(ii)$ The $H^{+}$ ions produced contribute to the proton gradient across the thylakoid membrane and are used to reduce $NADP^{+}$ to $NADPH$,which acts as a strong reducing agent in the biosynthetic phase.
$(iii)$ The electrons $(e^{-})$ released are transferred from $PS-II$ to $PS-I$ via the electron transport system,facilitating the synthesis of $ATP$ through photophosphorylation.