What causes the largest changes in melting point across period 2 elements? 1)change in bonding structure
2)greater electronegativity
3)greater number of electrons
4)increase in nuclear charge

Iam pretty sure that the answer is d

Van der waals forces are temporary electromagnetic forces established between uncharged atoms. some neutral molecules, when close together, can become temporarily “charged,” as electrons move around the atom. water is a polar molecule, the side of the molecule that the hydrogens bond to being more positive, and the opposite side bound to the lone pairs of electrons being more negative. this means that it participates in dipole-dipole interaction (non-polar exhibits dispersion forces), and it has the capacity for hydrogen bonding.