a) Falling liquid drops are spherical.
Due to surface tension. Surface tension is the property of liquid due to which it tries to aquire minimum surface area. Since, for a given volume sphere has a minimum surface area, a mercury droplet is spherical.
b) Evaporation takes place from the surface of liquid.
Since, the kinetic energy of the surface molecule is greater than the bulk molecule, evaporation takes place from the surface of liquid.
c) It is more efficient to wash clothes in hot water than cold water.
Surface tension decreases on increase in temperature. Due to this hot water can wet the clothes more effectively then cold water. So, it is more e to wash clothes in hot water than cold water