Historical clue formulations

• Argon or neon — 2025-07-29
• Xenon, e.g. — 2024-12-01
• It won't react well — 2021-06-05
• Noble thing — 2020-07-12
• He is one — 2019-12-21
• It's hard to get a reaction out of it — 2011-07-30
• Noble thing — 2008-12-12
• Krypton, e.g. — 2006-07-12
• Neon or helium — 2004-09-17