Which part of the liquid is responsible for the phenomenon of surface tension ?

Which phenomenon is responsible for the echo of sound wave?

Surface tension of a liquid is a molecular phenomenon of liquids involving the force of cohension along the liquid molecules. It is scalar quantity and is numberically equal to the surface energy. Numerically, it is proved that the potential soluble salts and surfce active substance. Sparingly soluble salts and surface acitve substances decrease the surface tension of the liquid. However, the fairly soluble solutes increase the surface tension of the liquid. Surface tension of a liquid is independent of surface area but it depends on the intemolecular forces and the temperature. Which among the following is not the unit of surface tension ?

_________ is a naturally occurring phenomenon that is responsible for the heating of the Earth's surface and atmosphere

Assertion : The impurities always decrease the surface tension of a liquid. Reason : The change in surface tension of the liquid depends upon the degree of contamination of the impurity.

A thin wire ring of radius of 2m is placed on the surface a liquid. If a force of 4N is required to pull this ring from the surface of liquid (before the liquid film breaks) then the surface tension of liquid is