| 2026-07-13 | Water or rust, chemically |
| 2026-06-28 | Rust, e.g. |
| 2025-01-22 | See 50-Down |
| 2024-09-08 | Laughing gas or quicklime |
| 2020-08-25 | Rust, chemically |
| 2019-04-14 | Water or rust |
| 2019-01-06 | Rust, e.g. |
| 2017-05-11 | Nitrous ___ |
| 2016-02-21 | Ethylene ___ |
| 2015-06-13 | Lime, e.g. |
| 2013-07-06 | Quicklime, e.g. |
| 2013-01-28 | Rust, for example |
| 2011-05-24 | Nitrous ___ |
| 2011-05-05 | Lime, e.g. |
| 2010-07-14 | Laughing gas, for one |
| 2010-05-29 | 6-Down, for one |
| 2010-03-16 | Water or rust |
| 2009-12-23 | Nitrous ___ |
| 2009-07-22 | Nitrous ___ |
| 2009-04-05 | Rust, for one |
| 2007-10-18 | Water, for one |
| 2005-11-13 | Rust, e.g. |
| 2005-08-31 | Rust, e.g. |
| 2004-11-15 | Nitrous ___ (laughing gas) |
| 2004-07-28 | Laughing gas, for one |
| 2004-04-06 | The O in FeO |
| 2003-05-21 | Rust, e.g. |
| 2001-12-25 | Nitrous ___ (laughing gas) |
| 2001-11-05 | Rust, e.g. |
| 2000-02-28 | Rust, for one |
| 1998-03-14 | Lime, for one |
| 1996-12-03 | Fe2 O3, e.g. |
| 1996-12-01 | Zinc ___ |