Final answer:
The frequency of a photon with an energy of 2.12 x 10^-22 J is 3.2 x 10^11 Hz.
Step-by-step explanation:
The energy of a photon can be calculated using the equation E = hf, where E is the energy, h is Planck's constant (6.626 x 10^-34 J·s), and f is the frequency of the photon.
Given that the energy of the photon is 2.12 x 10^-22 J, we can rearrange the equation to solve for f:
f = E / h
Plugging in the values, f = (2.12 x 10^-22 J) / (6.626 x 10^-34 J·s) = 3.2 x 10^11 Hz.
Therefore, the correct answer is (a) 4.5 x 10^9 Hz.