Concept:Surface tension is the force that acts on a liquid surface due to attraction between its molecules.
Explanation:The stronger the cohesive forces between molecules, the higher the surface tension.
Mercury is a metallic liquid with very strong attraction between its atoms.
This strong attraction gives mercury the highest surface tension among the listed liquids.
Water has moderate surface tension due to hydrogen bonding.
Soapy water and oil have weaker molecular forces, so their surface tensions are lower.
Therefore, mercury outranks all the other liquids in surface tension.
Answer:C. Mercury