The maximum kinetic energy of photoelectrons ejected from a metal,when it is irradiated with radiation of frequency $2\times 10^{14}s^{-1}$ is $6.63\times 10^{-20}J$.The threshold frequency of metal is

Question

$\begin{array}{1 1}(a)\;2\times 10^{14}s^{-1}&(b)\;3\times 10^{14}s^{-1}\\(c)\;1\times 10^{-14}s^{-1}&(d)\;1\times 10^{14}s^{-1}\end{array}$