Option 1 states that UV light is an electromagnetic wave. This is correct. UV light falls within the electromagnetic spectrum, just like visible light, radio waves, and X-rays.

Option 2 states that UV light can travel through a vacuum. This is also correct. Unlike sound waves, which require a medium to propagate, electromagnetic waves can travel through a vacuum.

Option 3 states that UV light is a longitudinal wave. This is not correct. Longitudinal waves are characterized by vibrations occurring in the same direction as the wave is traveling. UV light, like visible light, is a transverse wave, meaning the vibrations occur perpendicular to the direction of the wave.

Option 4 states that the wavelength of UV light is shorter/smaller than that of visible light. This is correct. UV light has a shorter wavelength than visible light, which is why it is often referred to as "ultraviolet" (beyond violet).

In conclusion, the correct statement is option 3, which states that UV light is a longitudinal wave. This is not correct. UV light is a transverse wave.