When a metal surface is exposed to a certain frequency of electromagnetic radiation,the kinetic energy of the electron ejected from the metal surface is $0.20 \ eV$. If its work function $(W_0)$ is $4.80 \ eV$,the approximate frequency of the radiation falling on the metal surface in $Hz$ is:

• A
  $1.98 \times 10^{15}$
• B
  $1.21 \times 10^{16}$
• C
  $1.21 \times 10^{15}$
• D
  $1.98 \times 10^{16}$