Provide an example of a spring for wave propagation.

Transverse waves can propagate in

Given below are some examples of wave motion. State in each case if the wave motion is transverse,longitudinal or a combination of both:
$(a)$ Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways.
$(b)$ Waves produced in a cylinder containing a liquid by moving its piston back and forth.
$(c)$ Waves produced by a motorboat sailing in water.
$(d)$ Ultrasonic waves in air produced by a vibrating quartz crystal.

Which type of waves can propagate in solids?

Transverse and longitudinal waves can propagate in solids,whereas only longitudinal waves can propagate in air. Explain this statement.

Which properties of a medium are required for the propagation of mechanical waves?