Question

Spreading of smell proves that _____
[A] Matter is made up of small particles
[B] The particles in matter are in motion
[C] Both [A] and [B]
[D] None of above

Answer 1

Hint: To answer this, you need to approach using the theory of diffusion. Gases are free to move in any direction i.e. they move randomly even though spread evenly. You can use this to answer the given question.

Complete answer:
We are well aware of the fact that smell spreads. When we spray a perfume or if someone is cooking something in the kitchen, the smell travels in other parts of the house too. To answer this question, we need to discuss why this happens.
Smell travels due to diffusion of particles from areas of higher concentration to that of lower concentration. Diffusion works when particles move around and thus this phenomenon is observed in liquids and gases as these particles.
Now, let us discuss diffusion in gases.
As we have already mentioned above, diffusion is observed due to difference in concentration. When we spray a perfume, the particles of the chemical substance in the perfume mix with the air particles. As gases have no particular direction they move in so it is free to move in all the directions and eventually spread throughout the place from areas of higher concentration i.e. from where it was sprayed to areas of lower concentrations i.e. other areas and thus we can smell it throughout.
However, the rate of diffusion varies with temperature and it is higher in hot gases. When we increase the temperature, the kinetic energy of gas increases i.e. the gas particles move faster thus diffusion will take place at a faster rate.
We have discussed above that gas particles as well as the smell move freely in all directions. However, the speed of the gas particles is much higher. The particles of smell collide with each other as well as air particles frequently and this causes change in their direction thus takes longer time to travel from one place to another. This random motion caused by collision is known as Brownian motion. This is also a proof that matter is made up of small particles which are always in motion.
We can understand from the above discussion that the matter is made up of small particles and the particles are always in motion.

Therefore, the correct answer is option [C] Both [A] and [B].

Note:
Diffusion also takes place in liquids as liquid particles can also move around. For example, if we put a crystal of potassium manganate (it is purple in colour) in a jar of water, the colour slowly spreads throughout the solution, hence causing purple colouration of the solution. This proves diffusion in liquids.