80.The mixing up of two gases as a result of random motion of molecules is
   (a) diffusion
   (b) effusion
   (c) vaporisation
   (d) sublimation
Ans: (a)
81.When a bottle of perfume is opened in one corner of a room the smell
   spreads soon throughout the room. This is an example of
   (a) surface tension
   (b) capillarity
   (c) viscosity
   (d) diffusion
Ans: (d)
82.When a bowler spins a ball, it changes its direction in the air. This is due to
   (a) turbulence caused by the wind
   (b) buoyancy of air
   (c) unequal pressures acting on it
   (d) sudden change in the direction of the wind
Ans: (c)
83.A capillary tube is partially dipped vertically in a vessel containing water.
   Due to capillarity water rises in the tube. The height of water rise in the tube
   can be increased by
   (a) decreasing the radius of the capillary tube
   (b) increasing the radius of the capillary tube
   (c) increasing the height of water in the vessel
   (d) None of these
Ans: (a)
84.The property of a fluid by which it resists relative motion within itself is
   known as
   (a) cohesive force
   (b) surface tension
   (c) diffusion
   (d) viscosity
Ans: (d)