why do strong bonds exist between water molecules?
they have nonpolar structure.
they are held together by hydrogen bonds.
the hydrogen end of a water molecule is weakly negative.
the shared electrons are more attracted to the hydrogen atom.

They are held together by hydrogen bonds.

Explanation:

H2O has very strong intermolecular forces known as hydrogen bonds because the hydrogen is bonded to oxygen, a highly electronegative element

Option (b) is the correct answer.

Explanation:

When a hydrogen atom is bonded to an electronegative atom then bonding between the combining atoms is known as hydrogen bonding.

For example, in a water molecule due to difference in electronegativity of oxygen and hydrogen atoms there will be development of partial negative charge on oxygen atom and partial positive charge on hydrogen atom.

As a result, the water molecule will become polar in nature. And, due to opposite charges on both hydrogen and oxygen atoms there will be strong bonds between the water molecules.

Hence, we can conclude that strong bonds exist between water molecules because they are held together by hydrogen bonds.