Awater molecule gains enough energy to enter the gas phase is chemical or physical? why?

It is a physical change becasue the chemical makeup of the water molecule did not change - the molecule just changed state.

Happy to help!

n has four pairs of electrons in the valence shell, electrons repel one another ,n has 7 protons in its nucleus, and since n has 7 protons, it must fill the second shell, giving it 4 pairs of electrons. the electrons form 3 bonds and 1 lone pair of electrons. each pair of electrons repels the other pairs, so they are equally far apart.

so all of the above