is a particle that frequently comes at the end of sentences in Japanese, and carries the same meaning as a question mark in English. (It is not limited to appearing at the end of sentences, however). In addition to questions, か
can also express uncertainty about something, without strictly being a question.
Is this a cup? (Plain question)
Is your apartment big? (Plain question)
I don't know if this is good or bad. (Expressing uncertainty, but not a question)
I don't know what this is. (Expressing uncertainty, but not a question)
regularly comes after the polite form of words, such as ～ですか
. However, in casual conversation か
can be used directly after the word that the speaker is showing uncertainty about.
Both examples are grammatically correct, but the sentence without です
may be considered rude by some people (as it sounds too familiar/direct).