Answer
$3.28\times10^{15}Hz$
Work Step by Step
The minimum energy of the photon is 13.6 eV because it must ionize the hydrogen atom. Find the minimum frequency using equation 27–4.
$$E=hf$$
$$f=\frac{E}{h}=\frac{(13.6eV)(1.60\times10^{-19}J/eV)}{6.63\times10^{-34}J \cdot s}$$
$$f=3.28\times10^{15}Hz$$