What type of pollution is caused by the working of mixer and grinder in the kitchen?

When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. Why?

Why sound cannot travel through vacuum (or through outer space)?

Why should we not put a pin or pencil in our ears?

Name any two common musical instruments and identify their vibrating parts.