A transverse wave travels along the Z-axis,the particles of the medium must move
In a transverse wave particles oscillate about their mean position perpendicular to the direction of motion of the wave. Now this wave is going along
Z-axis therefore the particles have to oscillate along direction perpendicular to Z-axis.
That could be any direction on the X-Y plane
b and c are not the correct answers as the question asks about a direction in which particle Must Move. 'Must'