Elements
- 281
- USGS Minerals Information: Nitrogen
- Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
- 282
- WebElements: Nitrogen
- Extensive information on history, uses, occurrence, compounds, and properties of the element.
- 283
- Wikipedia: Nitrogen
- Properties of the element, including its history, applications, and characteristics.
- 289
- WebElements: Osmium
- Extensive information on history, uses, occurrence, compounds, and properties.
- 290
- Wikipedia: Osmium
- Properties of the element, including its history, applications, and characteristics.
- 294
- WebElements: Oxygen
- Information on history, uses, occurrence, compounds, and properties of the element.
- 295
- Wikipedia: Oxygen
- Properties of the element, including its history, applications, and characteristics.