“How fast do X rays travel in a vacuum?

299,792,458 meters per second

(But but, but that's the speed of light !)

(It sure is ! And also the speed of radio, infrared, visible light, ultraviolet light, X-rays and gamma rays. All uvum !)

the answer is definitely c.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.