# Calculate the angular frequency of an electron occupying the second Bohr's orbit of $He^+$ ion.
$\begin{array}{1 1}(a)\;2.067\times 10^{16}sec^{-1}&(b)\;1.32\times 10^{16}sec^{-1}\\(c)\;2.067\times 10^2sec^{-1}&(d)\;3.2\times 10^{20}sec^{-1}\end{array}$