Question

The surface tension of lyophilic sols is
(1) lower than that of $ H_2O $
(2) more than that of $ H_2O $
(3) equal to that of $ H_2O $
(4) either less or more than $ H_2O $ depending upon the nature of the disperse phase.

Answer 1

Hint: The effect known as surface tension is caused by the cohesive forces between liquid molecules. Since the molecules at the surface lack like molecules in both directions, they cohere more closely to those specifically aligned with them on the surface. This creates a surface "film" that makes moving an object across the surface more difficult than moving it while fully submerged.

Complete answer:
Lyophilic sols are those that are generated directly by mixing substances in an appropriate dispersing medium. Lyophilic sols are very stable, with heavy interactions between the distributed phase and the dispersion medium. Since the dispersion medium can be separated from the colloid by evaporation, they are also known as reversible sols.
Rubber and starch are two examples.
Lyophilic sols are those with a high affinity for the dispersion medium and thus easily form colloidal solutions. They have a lower surface tension than the dispersion medium and their viscosity reduces as they become more hydrated.
Since lyophilic colloids have a high affinity for the water solvent, which reduces surface tension, the surface tension of lyophilic sols is lower than that of water.
The surface tension of lyophilic sols is smaller than that of water because lyophilic colloids have a high affinity for the water solvent, which reduces surface tension.

Note:
Lyophobic sols are not formed merely by mixing the compounds and the dispersion medium. These sols are not stable; they readily coagulate when a small amount of electrolyte is added to them, or when they are heated or shaken. Because of the adsorption of ions by the scattered particles, lyophobic sols may be stabilised. They have an irreversible existence.
Dissolved ferric hydroxide or aluminium hydroxide in water, are examples.