I would go with C because that seems like the best answer choice
No, x-rays do not travel slower than infrared radiation or even the opposite. Both are travelling in vacuum therefore they travel at same speed. They differ in the frequency of the electromagnetic waves.
Hertz is units for frequency. (waves per second)
wavelength = speed/frequency
if you're given the speed use that to calculate, if not then you can probably assume it's a wave of light and use the speed of light (3x10^8 m/s) to calculate.
wavelength = (3x10^8)/(1.28x10^17)
= 0.000000002 m
= 2.34 nm
It will lose them and become stable
