The particle 'か' is placed at the very end of a sentence to form a question. It is used in both polite and casual speech, but it is especially common in polite conversation because it adds a clear interrogative tone without being abrupt. For example, '行きます' (I will go) becomes '行きますか' (Will you go?). In casual speech, you might omit 'か' and use rising intonation instead, but using 'か' is always correct and clear.

When the sentence ends with a noun or a な-adjective, you need to include 'だ' before 'か' in casual speech (e.g., 学生だ → 学生か), but in polite speech you use 'です' (e.g., 学生ですか). For verbs and い-adjectives, no extra copula is needed; just attach 'か' to the plain form or polite form.

Note: The character 'か' also appears as a different grammar point meaning 'or', 'subject marker', or 'but', but when it appears at the end of a sentence with rising intonation, it is the question particle. Context will usually make the meaning clear.