Which of the following best describes cobalt(II) oxide?

• A. It is an organic compound used as a fuel.
• B. It is a colorless gas formed by the combustion of cobalt.
• C. It is a blue liquid commonly found in batteries.
• D. It is an inorganic compound with the formula CoO, appearing as a black solid.

Answer: (D)

Verified step by step guidance

1. Identify the nature of cobalt(II) oxide by analyzing its chemical composition and properties. Cobalt(II) oxide consists of cobalt and oxygen atoms, which classifies it as an inorganic compound.
2. Recall that organic compounds primarily contain carbon atoms bonded to hydrogen, oxygen, nitrogen, or other elements. Since cobalt(II) oxide does not contain carbon, it is not an organic compound.
3. Consider the physical state and appearance of cobalt(II) oxide. It is known to be a solid at room temperature, typically appearing as a black powder or solid, not a gas or liquid.
4. Understand that cobalt(II) oxide has the chemical formula \(\mathrm{CoO}\), indicating a 1:1 ratio of cobalt ions (Co\(^{2+}\)) to oxide ions (O\(^{2-}\)).
5. Conclude that the best description is that cobalt(II) oxide is an inorganic compound with the formula \(\mathrm{CoO}\), appearing as a black solid.