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

Assertion $(A) :-$ The whole scheme of transfer of electrons starting from $PS-II$ to $NADP^{+}$ is called $Z-scheme$.
Reason $(R) :-$ When all the carriers of this scheme are placed in sequence on a redox potential scale,they appear like $Z$.
In the light of the above statements,choose the correct answer from the options given below:

In the light reaction of photosynthesis,chlorophyll is subjected to

In the grana,the process $ADP + P_i = ATP$ is called .........

$ADP + \Pi = ATP$ formation in grana is called......

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