Observation

performance was average in this question. Some candidates however, in error failed to uphold the idea of cohesion and adhesion between the molecules of mercury or molecules of glass or water by slipping the salient word ‘molecules’ in their explanation.  Some lost marks because they considered cohesion between molecules of mercury to be lesser than adhesion between mercury and glass.

The expected answer is :

Cohesion between molecules of mercury is greater than adhesion between the molecules of mercury and that of glass; (hence mercury does not wet glass). While Cohesion between molecules of water is less than adhesion between the molecules of water and that of glass; (hence water wets glass).