Answer 1

(c) the intensity remains unchanged
(d) the minimum wavelength decreases

Cutoff wavelength (`λ_min`) is given by 

`λ_min = (hc)/(eV)`

Here,
h = Planck's constant
c = Speed of light
V = Accelerating voltage
e = Charge of electron

If the potential difference applied to an X-ray tube  (V) is increased, then the minimum wavelength (cutoff wavelength) gets decreased.
Intensity is not affected by the potential difference applied.