The gas released in photosynthesis is

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 $ATP$

Chemiosmosis explains .......

Photophosphorylation differs from oxidative phosphorylation in requiring input of energy in the form of

Why do proton gradients form across the thylakoid membrane during the light reaction of photosynthesis?

The first step of photosynthesis is: