Which of the following photosynthetic pigments is responsible for the photolysis of water,leading to the release of molecular oxygen?

The following $(I-VI)$ are the main steps of chemiosmotic $ATP$ synthesis in the light reaction. Arrange them in the correct order:
$I$. $H^+$ concentration gradient established
$II$. $H^+$ diffuses through $ATP$ synthase
$III$. Carriers use energy from electrons to move $H^+$ across the membrane
$IV$. Electrons from $PS-II$ pass along the electron transport chain
$V$. Light excites electrons in $PS-II$
$VI$. Energy of $H^+$ flow is used by $ATP$ synthase to make $ATP$

The water splitting complex is associated with

The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction?

$DCMU$ ($3$-($3$,$4$-dichlorophenyl)$-1,1-$dimethylurea) is a chemical that acts as an inhibitor of photosynthesis. What is its specific mode of action?

In the photosynthesis process,which molecule acts as the reaction center?