What sound does /ɔɪ/ represent?

The sound /ɔɪ/ represents the diphthong found in the word "boy." It consists of two vowel sounds that glide together, starting from a mid-open back rounded position and moving towards a near-front close position. This specific sound combines the qualities of the /ɔ/ sound, which is typically associated with words like "caught," with the /ɪ/ sound, as in "bit."

In contrast, the other options involve different vowel sounds or combinations that do not match the characteristics of /ɔɪ/. The sound in "girl" is represented by a different vowel sound entirely, typically transcribed as /ɜr/ or /ɪr/, depending on the accent. The sound in "bed" corresponds to the vowel /ɛ/, and "sun" features the vowel /ʌ/, both of which are distinct from the diphthong /ɔɪ/. Therefore, "boy" is the only word in the choices that accurately reflects the sound represented by /ɔɪ/.