Which factor is most responsible for the fact that water is a liquid rather than a gas at room temperature?
a. van der waals forces
b. hydrogen bonding
c. london dispersion forces
d. ionic bonding

The answer is B. hydrogen bonding

Explanation:

The liquid state of water is due to the fact that its molecules are joined together by hydrogen bonds. This molecular attraction is much more intense than the attractions due to the Van der Waals forces that bind the molecules of a gas. This makes the water liquid under normal conditions.

Hydrogen bonds are formed when in the molecule, a hydrogen atom is attached by a covalent bond to a small and very electronegative atom (F, O or N). Then the pair of electrons in the bond moves, in this case, to the oxygen atom because it is the most electronegative atom, a negative partial charge appearing on it and a positive partial charge on the hydrogen atom. This formed dipole causes the positive pole of one of the water molecules to be electrostatically attracted by the negative pole and pair of non-shared electrons of the oxygen atom of another neighboring molecule. Then each molecule is tetrahedrally linked to four neighboring molecules.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)