What are the products of the Hill reaction?

The Emerson enhancement effect and the red drop phenomenon were instrumental in the discovery of which of the following?

Which of the following occurs during the light reaction of photosynthesis?

Proton gradient is very important across the membrane because

Which are incorrect sentences for non-cyclic photophosphorylation?
$(1)$ $Z$ shape is formed when all the carriers are placed in a sequence on a redox potential scale.
$(2)$ The $4e^-$ released are accepted by various electron acceptors and finally enter into $PS-II$ instead of returning to $PS-I$.
$(3)$ In this process both $PS-I$ and $PS-II$ take part.
$(4)$ As the electrons released in various ways do not return to their original donors,such an electron transport is called non-cyclic electron transport.

Which pigment acts as the reaction center during photosynthesis?