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 $\mathrm{Ca}^{2+}$.