a) The correct answer is
C blue
In fact, we see from the electromagnetic spectrum in the figure that light with wavelength of 480 nm corresponds to blue light.
b) The correct answer is
C shorter, higher
In fact, microwaves have wavelengths between 0.1 cm and 1.0 m, while radio waves can have wavelength of several metres, so microwaves have shorter wavelength than radio waves. Since the frequency of a wave is inversely proportional to its wavelength, this also means that microwaves have higher frequency than radio waves.
