Which is the smallest unit of sound in a language that can change meaning?

• A. Phoneme
• B. Morpheme
• C. Allophone
• D. Grapheme

Answer: (A)

The main idea here is how meaning is distinguished by tiny sound units. The smallest unit of sound that can change meaning is a phoneme. Phonemes are the mental categories of sounds that people treat as contrastive; when you swap one phoneme for another, you typically get a different word with a different meaning. For example, the sounds /p/ and /b/ distinguish words like “pat” and “bat.”

In contrast, allophones are just different ways the same phoneme can be pronounced without changing meaning, so they don’t create new words. Morphemes, on the other hand, are the smallest units of meaning themselves, not sounds—things like "un-", "happy", or "-ness." Graphemes are the written symbols that represent sounds, not the sound units themselves.