If a question received on the Q&A tool is irrelevant you can choose to Archive the question. A publicly answered question can also be archived. This will ensure that it is not displayed at the front end any more. The option to Archive can be seen below the question.
Note - The Privately Answered questions also have the option to Archive.
Once archived you can choose to move the question to the Junk folder. Only when answered can a question either be archived or junked.
From the Junk folder, you can delete the question at any time, by clicking on Delete.
Delete will permanently remove the question.
Note - At any point before deletion you can click the Restore link to put the question back to where it was before.