Which of the following best describes the appearance of copper(II) oxide?

• A. A green solution
• B. A red metallic solid
• C. A black solid
• D. A blue crystalline powder

Answer: (C)

Verified step by step guidance

1. Understand that copper(II) oxide (CuO) is an inorganic compound formed by copper and oxygen where copper is in the +2 oxidation state.
2. Recall the typical physical appearance of copper(II) oxide, which is commonly known from laboratory observations and chemical literature.
3. Recognize that copper(II) oxide is not a solution but a solid, so options describing a solution can be eliminated.
4. Note that copper(II) oxide is not metallic in appearance, so the red metallic solid option is incorrect.
5. Conclude that copper(II) oxide is best described as a black solid, distinguishing it from other copper compounds like copper(I) oxide (which is red) or copper(II) salts (which can be blue or green).