Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Polyatomic ion:

This text is part of the article's lead section, so referencing it may be optional. Please see WP:CITELEAD for more information.

"

In older literature, a polyatomic ion may instead be referred to as a radical (or less commonly, as a radical group). In contemporary usage, the term radical refers to various free radicals, which are species that have an unpaired electron and need not be charged.[citation needed][3]