In which type of wave do particles of the medium move in small circles?
a surface wave
b transverse wave
c longitudinal wave
d none of the above

a. Surface wave

Explanation:

Waves propagate energy in a medium and the energy in a wave is being transferred by the particles in the wave. Here, there are three types of waves are given. Let's start with the Longitudinal waves, in this type of waves the particles in the wave vibrate back and forth but moves in a parallel direction of the propagating wave. Transverse waves are characterized by the perpendicular motion of the particles in comparison with propagating wave.  Surface wave's particles move in small circles because the particles vibrate in all directions, back and forth and up and down. Hence, the Surface wave is the answer.