Answer:
they are the same element because they have the same number of protons and electrons,but a different number of neutrons
The density of ice is less than the density of water.
Fun fact: Water is the only known liquid that has this change it density.
There are no states in the picture, but Na should have a "(s)" after it, and Cl2 should have a "(g)" after it. NaCl should have an "(s)". Chlorine is a diatomic element so it has a "2" subscript on it.
Hope this helped! :)