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The first sentence is wrong. It can also be a non pure state. --2001:16B8:490B:FF00:71BC:F049:F089:5A4F (talk) 23:48, 23 January 2020 (UTC)[reply]

This article was the subject of a Wiki Education Foundation-supported course assignment, between 19 August 2024 and 13 December 2024. Further details are available on the course page. Student editor(s): B512251, B125181 (article contribs). Peer reviewers: Jbradmitchell, Zhuguang Chen.

— Assignment last updated by Phyhuan (talk) 04:11, 13 December 2024 (UTC)[reply]