An electric bell is kept under a bell jar in which a vacuum has been created. slowly air is introduced in to the jar. what will happen to the sound of the electric bell?

It will increase and will attain a certain highest value.

Explanation:

An electric bell is kept under a bell jar with vacuum and on introduction of air into the jar we are providing medium. This medium helps the sound to travel faster. Sound is defined as vibration of medium so if medium is provided it will travel faster.

It is characterized as mechanical wave, so it propagates as oscillation of medium.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.