Question

A bottle of perfume is opened in the corner of a large hall of volume 1000 $m^3$ . After some time, the whole hall smells of the perfume.
Which of the following properties of gas is responsible for this observation?
(A) Thermal conductivity
(B) Viscosity
(C) Diffusion
(D) Compressibility

Answer 1

To answer this question, you must recall the characteristic properties of gases. The process by which the smell of perfume spreads in the entire hall is a phenomenon in which gas molecules move from an area of high density to an area of lower density of the gas.

Complete step by step solution:
We know from the kinetic molecular theory of gases that the particles of any given substance are always in constant motion at any temperature above the absolute zero. In case of solids, since the particles are strongly bound together, the motion of the particles is in the form of vibrations at a fixed position. On the other hand, in liquids and gases, since the intermolecular forces are low, the particles can move around.
We know that perfumes are very volatile, i.e. it changes from liquid state to vapours at a very low temperature. When the bottle of perfume is opened in the corner of the large hall, the tiny particles of the perfume, evaporate and atomize in the air. Then these gas particles start moving around, diffusing into the atoms of the air present throughout the hall slowly spreading all across the hall. Thus, the property responsible is diffusion. The perfume particles diffuse from a region of high concentration, i.e. the corner of the hall to the regions of lower density, i.e. the rest of the hall, spreading uniformly throughout.
Thus, the correct answer is C.

Note:
Solids are rigid and have a definite volume. The diffusion rate of solid particles is the least while that in gases is the highest. In case of solids, since the particles are strongly bound together, the motion of the particles is in the form of vibrations at a fixed position. On the other hand, in liquids and gases, since the intermolecular forces are low, the particles can move around.