Which one of the following is essential for photolysis of water?

Photolysis of water requires light energy, and oxygen evolving complex (OEC) and an electron carrier $Y_z$. OEC complex was formerly called Z-enzyme. It has four Mn ions. Light energy brings about changes in $\mathrm{Mn}$\left(\mathrm{Mn}^{+2}, \mathrm{Mn}^{+3}, \mathrm{Mn}^{+4}\right)$which helps in removing electrons from$\mathrm{OH}^{-}$component of water forming oxygen. Liberation of oxygen also requires$\mathrm{Cl}^{-}$and$\mathrm{Ca}^{2+}.