Assertion $(A) : H^+$ gradient across the thylakoid membrane is essential for the formation of $\text{ATP}$.
Reason $(R) :$ Breakdown of $H^+$ gradient due to the movement of protons through $F_0$ of $\text{ATP}$ synthase releases enough energy to activate $\text{ATP}$ synthase enzyme that catalyses the formation of $\text{ATP}$.

• A
  $A$ and $R$ are true and $R$ is the correct explanation of $A$.
• B
  $A$ and $R$ are true but $R$ is not the correct explanation of $A$.
• C
  $A$ is true,$R$ is false.
• D
  $A$ is false,$R$ is true.