Sound cannot propagate in _________________________.
A. Vacuum
B. Solid
C. Liquid
D. Gases

Hint: In this question, we know that sound is able to propagate through any medium because of the pressure variation causing alternating rarefaction and compression of the sound particle in the medium like in air, gas, and solid. But in a vacuum, we don’t find particles in which this pressure variation could take place and hence sound is also not propagated in sound.

Complete Step-by-Step solution:
Sound waves are always caused by a source and it propagates by making the particles in the medium vibrate. This sound source transfers the vibrations to the particles surrounding it in the medium. The medium can be solid, liquid, gaseous, or plasma. These vibrating particles cause rarefaction and compression which create a pressure variation in the surrounding region in the medium. Now, this process of alternating compression and rarefaction helps the sound waves to propagate as can be seen from figure 1.




In short, we can say that when the sound waves propagate in a medium the particles gain these vibrations and then transfer them to the surrounding particles, allowing sound to travel.
Whereas in a vacuum as there are no particles to vibrate, therefore there is no pressure variation in the surrounding, so sound cannot travel. We can see an example for the same that is in the near-vacuum region in outer space which is practically not a complete vacuum region and there are minute amounts of gas particles which can help in the propagation of sound. But, the density of these gases is much lesser than the earth's atmosphere, which causes less sound and even though the sound is propagating our ears are not sensitive enough to detect this sound, and therefore we consider space as soundless.
So the correct answer is option A.

Note: For solving these types of questions we need to be well versed with some basic concepts of sound and light. We also need to know how these behave in different mediums like in gas, liquid, solid, and vacuum. It's also important to understand how different parameters affect these two waves like temperature, pressure, refractive index, and density of the particle.