In radio communication, how is the number "4" expressed phonetically?

In radio communication, especially in aviation and maritime contexts, using a standardized phonetic alphabet is crucial for ensuring clarity and avoiding misunderstandings. The number "4" is pronounced phonetically as "FOUR", which is represented as "FOW ER" in the context of this question to capture the essence of its pronunciation.

The phonetic spelling helps to avoid confusion that might arise from similar-sounding numbers when transmitted over radio. This practice is part of a broader system known as radiotelephony, where numbers and letters are communicated in a way that reduces the risk of error in noisy environments. By using "FOW ER", it allows operators to distinctly convey the numeral without ambiguity.

In contrast, the other provided options do not correctly represent the phonetic expression for the number "4". "THREE" refers specifically to the number 3, "TOO" corresponds to 2, and "FIVE" indicates the number 5. Consequently, none of these options fulfill the requirement of representing the number "4" phonetically.