Which of them are not monobasic acid?
A monobasic acid is an acid that has only one hydrogen ion to donate to a base in an acid-base reaction. Therefore, a monobasic molecule has only one replaceable hydrogen atom. In case of, nitric acid, hydrochloric acid and hydrobromic acid there are one replaceable hydrogen ion. In carbonic acid, there are two replaceable hydrogen ions and hence it is dibasic.