Choose all the answers that apply. light slows down when traveling through more dense substances does not require a medium to travel through can be absorbed and transformed into heat speeds up when traveling through less dense substances is refracted when it changes direction and speed travels in longitudinal waves

is created by vibrations in electric and magnetic fields. does not require a medium.   travels in longitudinal waves.

Explanation:

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.