Read the following options and select which is not a longitudinal wave.  

• Longitudinal waves are waves where the displacement of the medium is in the same direction as the direction of the travelling wave.
• For example, all types of sound waves and seismic waves occur during earthquakes.
• Light is an example of a transverse wave. 
• When it comes to transverse waves in matter, the displacement of the medium is perpendicular to the direction of propagation of the wave. 
• For example, a pond ripple or a wave on a string.

Therefore, we can say that light is not a longitudinal wave.