Answer
$f = 1.23\times 10^{20}~Hz$
Work Step by Step
In part (b), we found that $\lambda = 2.43\times 10^{-12}~m$
We can find the frequency:
$f = \frac{c}{\lambda}$
$f = \frac{3.0\times 10^8~m/s}{2.43\times 10^{-12}~m}$
$f = 1.23\times 10^{20}~Hz$
