Remember that λ, or wavelength, is proportional to (1/f), where f=frequency. That means that wavelength and frequency are inversely related. When one goes up, the other goes down, and vice versa. That means answers C and D are incorrect because those answers have wavelength and frequency in a direct relationship.
Radiant energy is directly proportional to frequency. When frequency increases, radiant energy increases. That means A) As wavelength decreases, radiant energy and frequency increase is the correct answer.
