Answer:

Introduction:
In this question, we are asked to identify the colour of copper oxide among four options. Copper oxide is a compound formed by the combination of copper and oxygen. The colour of copper oxide depends on the type of copper oxide and the method of preparation.

The colour of copper oxide:
The correct answer to this question is black. Copper oxide is generally black in colour. However, the colour of copper oxide can vary depending on the type of copper oxide.

Types of copper oxide:
There are two main types of copper oxide: cuprous oxide (Cu2O) and cupric oxide (CuO).

Cuprous oxide:
Cuprous oxide is a red or reddish-brown powder. It is also known as red copper oxide. When cuprous oxide is heated, it decomposes to form cupric oxide and copper.

Cupric oxide:
Cupric oxide is a black powder. It is also known as black copper oxide. Cupric oxide is formed when copper is heated in the presence of oxygen.

Conclusion:
In conclusion, the colour of copper oxide is black. Copper oxide is a compound formed by the combination of copper and oxygen. The colour of copper oxide can vary depending on the type of copper oxide. Cuprous oxide is a red or reddish-brown powder, while cupric oxide is a black powder.