Assertion: Two persons on the surface of the moon cannot talk to each other. Reason: There is no atmosphere on the moon. A) Both assertion and reason are true and reason is the correct explanation of assertion. B) Both reason and assertion are true but reason is not the correct explanation of assertion. C) Assertion is true and reason is false. D) Assertion is false but reason is true.
Hint: When there is no atmosphere, sound waves cannot travel and thus we can hear each other on the surface of the moon. Sound waves need a physical medium to travel through. Sound waves propagate by compression and then lengthening, this process keeps on repeating for the sound wave to travel. Using the above mentioned logic we will state the reason behind non travelling sound waves in vacuum.
Complete answer: The moon has no tangible atmosphere at its surface, it is a near vacuum. Sound waves are pressure waves that propagate by vibrating the molecule of a medium, such as air or water. In a vacuum, there is nothing to vibrate, and thus no propagation. When we speak, we use our mouth to create vibrations in the air in our mouth. That air passes the vibration to the air just outside our mouth, which passes the vibration to the air next to it, and so on, until it reaches the air in our ears, which pass the vibration to our eardrums. Sound waves are compression waves, which means it requires propagation through compression and then lengthening the relative distance between the two adjacent particles in a medium. In the vacuum of space, particles are too far apart to interact with each other, and so moving one particle doesn't affect the one down the line. Thus the reason and assertion are both true and reason is the correct explanation of assertion.
Therefore, Option (A) is correct.
Note: Unlike sound waves Electromagnetic waves can travel through the vacuum of space. Electromagnetic waves do not require any medium to travel other than space itself. So, astronauts on the surface of the moon talk to each other by using radio, radio waves are electromagnetic waves and thus can be easily transmitted on the surface of the moon.