When voting to close (or flagging to close) a question on Stellar the only options are "Off topic" and "Belongs elsewhere" - as shown in the screenshot below.
The facility exists on sites to add a few site-specific close reasons. The Stellar site has existed for long enough now that the community should be able to come up with some good reasons.
There is an "Other" reason on the dialogue, where you can type a custom message for your reason to close. However, regularly used reasons should have their own entry for simplicity and consistency.
Please add some suggestions below, and those with highest votes will be added in due course.