Answer
(a) stay the same
(b) III
Work Step by Step
(a) We know that in x-ray tube, the wavelength of the characteristic x-rays remains the same if the energy of the electrons striking the target is increased.
(b) We know that the best explanation is option (III) -- that is, the wavelength of characteristic x-rays depends only on the material used in the metal target, and does not change if the energy of incoming electrons is increased.
