Assertion $(A) :-$ The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.
Reason $(R) :-$ The work function of the metal varies as a function of depth from the surface.

• A
  Both $(A)$ and $(R)$ are correct but $(R)$ is not the correct explanation of $(A)$
• B
  $(A)$ is correct but $(R)$ is not correct
• C
  $(A)$ is incorrect but $(R)$ is correct
• D
  Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$