か

か is the primary question-forming particle in Japanese.

Functions

1. Yes/No questions: 行(い)きますか (Are you going?)
2. WH-questions: 何(なん)ですか (What is it?)
3. Alternative questions: Aか B (A or B)
4. Embedded questions: …かどうか (whether…)

Common patterns

• Sentence + か: direct question
• A か B: A or B
• Verb/Adj + か + どうか: whether or not
• Question word + か: embedded question

WITH POLITE VS. PLAIN FORMS: か is standard after です and ます forms, where it is the normal, neutral way to ask a question. After plain forms it is much less common in everyday conversation and can sound blunt, literary, or challenging (行(い)くの? is the usual casual question instead).

AかB VS. AかBか: with two nouns, コーヒーか紅茶(こうちゃ) is the ordinary pattern; repeating か after the second option (行(い)くか行(い)かないか) is normal when the alternatives are clauses, and sets up a choice the listener is asked to resolve.

Note: In casual speech, か may be omitted and replaced by rising intonation alone. In very casual male speech, か can sound blunt.