What do you call an interaction that holds two atoms together?

How will the system respond to a temperature increase?

Light traveling in water, nwater = 1.33, strikes a plastic block at an angle of incidence of 51.4°; part of the beam is reflected and part is refracted. if the index of refraction of the plastic is 2.0, what is the angle made by the reflected and refracted beams?

This is the number of complete movements of a wave per second.