Which of the following is an example of a word without an onset?

A word without an onset is characterized by the absence of consonants at the beginning of the word. In this case, the word "I" stands out as it is a single vowel sound with no preceding consonant.

The other options contain initial consonants that qualify them as having onsets. For instance, "Tree" begins with the 't' sound, "Sky" starts with the 'sk' blend, and "Stop" begins with the 'st' blend. Since "I" lacks any consonant at the start, it is accurately identified as a word without an onset. Understanding onsets can be important for phonological awareness and literacy development, particularly for young learners or those learning English as a second language.