Which type of wave exhibits an up and down motion or is at right angles to the direction of travel?

The wave that exhibits an up and down motion or moves at right angles to the direction of travel is a transverse wave. In transverse waves, the oscillations occur perpendicular to the direction of wave propagation. This means that as the wave travels horizontally, the motion of the particles in the medium moves vertically, creating the characteristic "up and down" movement.

Common examples of transverse waves include waves on a string and electromagnetic waves, such as light. The up-and-down motion can be visualized when considering how a string vibrates when plucked: the displacement of the string moves between higher and lower positions, forming crests and troughs.

Longitudinal waves, in contrast, have oscillations that occur parallel to the direction of travel, which is not the case described in the question. Mechanical waves can be either longitudinal or transverse, while electromagnetic waves specifically refer to a category that includes transverse waves but does not define the up and down motion characteristic alone. Therefore, the correct identification of the type of wave in question is indeed transverse.