why zwitterion is called internal salt?
In chemistry, a zwitterion (/ˈtsvɪtəˌraɪən/ TSVIT-ə-rye-ən; from German Zwitter [ˈtsvɪtɐ], meaning 'hermaphrodite'), also called an inner salt, is a molecule that contains an equal number of positively- and negatively-charged functional groups.