Between ac and dc, which is more dangerous? if so, what makes it dangerous?

AC is more dangerous because the chance of a human suffering from Ventricular Fibrillation is much higher in the case of AC than DC. On the other hand, the impedance for DC is higher compared to AC so the harshness of electric shock would be comparatively lower than AC. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

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.