Answer:
Surface tension is the downward force acting on the surface of liquid due to presence of inter molecular forces or cohesive forces between the particles of liquid.
Surface tension decreases with increase in temperature as the forces among particles decrease due to increase in kinetic energy and thus the cohesive nature decreases and thus surface tension also decreases.
Surface tension may decrease or increase with increase in soluble impurities .Insoluble impurities decrease the surface tension.
