Which of the following is a correct pair of singular and plural?

The correct answer is Option (2) → Stereo:Stereos

The correct pair of singular and plural is:

☀ Stereo:Stereos

Explanation for each option:

☀ Phenomenon:Phenomenons: This is incorrect. The correct plural form of "Phenomenon" is "Phenomena."

☀ Stereo:Stereos: This is correct. The singular form of "Stereo" is "Stereo," and the plural form is "Stereos."

☀ Reef:Reef: This is incorrect. The plural form of "Reef" is "Reefs."

☀ Axis:Axises: This is incorrect. The correct plural form of "Axis" is "Axes."