Question

What is the reason behind the high surface tension of water?

Answer 1

Water is a very polar molecule.

This means there is a (slight) difference in charge between the ends of the water molecule. Water is made up of an Oxygen and two Hydrogens (H₂O). The Oxygen is a much larger atom, with 8 protons in its nucleus, whereas Hydrogen has only 1 proton.

As protons are positively charged, the oxygen has a greater positive charged, so the electrons which are negatively charged are more attracted to the Oxygen, and the bond shifts slightly towards the oxygen. As the electrons have shifted position, the negative charge has shifted position, to there is a slight negative charge nearer the Oxygen, δ⁻ (delta minus), and a slight positive charge, δ⁺ (delta plus), at the Hydrogen.

This allows strong inter molecular forces to occur, as the slightly positive Hydrogens are attracted to the slightly negative Oxygens. This force of attraction between water molecules causes them to want to 'stick together', causing a high surface tension.

So the answer is B)

Answer 2

The polarity of the water molecule helps it to cohere to nearby water molecules, forming a skin over it.