Which of the following media does NOT belong to the group?

The choice of optical fiber as the media that does not belong to the group is correct based on the properties and functions of each option.

Sea water, air space, and vacuum are all related to the transmission of waves, particularly sound and electromagnetic waves. Sea water and air conduct sound waves, while vacuum, although lacking a medium for sound, allows electromagnetic waves to propagate, such as light.

On the other hand, optical fiber specifically refers to a medium designed primarily for the transmission of light (an electromagnetic wave) through a material. It does not have the same capability as the other three options for conducting sound or being a physical medium that supports propagation of waves in a traditional sense.

Thus, given these distinctions, optical fiber stands out as the medium that does not conform to the same category of wave transmission as the others listed.