吗
ma · HSK 1
particle: calling for agreement or disagreement
口 mouth + 马 horse (phonetic mǎ) — mouth-particle for yes/no questions
吗 ends a statement to turn it into a yes/no question, like adding a spoken question mark. The 口 radical marks it as a speech particle; 马 (mǎ) just lends the sound.
吗 — mouth radical 口 + horse 马 (phonetic)
吗 is a phono-semantic compound. The mouth radical 口 signals it relates to speech, while 马 (mǎ) supplies the sound. It is a modern grammatical particle used to turn a statement into a yes/no question, with no pictographic meaning of its own.