The correct option is Copper(II) oxide.
Explanation
Metals react with oxygen to form metal oxides. The reactivity and the nature of the oxide formed depend on the specific metal and the conditions of the reaction, such as temperature.
Detailed Analysis:
- Reaction of Copper with Oxygen: Copper is a reddish-brown metal. When heated in air, it does not burn (unlike magnesium) but undergoes a surface reaction with atmospheric oxygen.
- Formation of Copper(II) Oxide: The copper surface becomes coated with a black layer of Copper(II) oxide ($CuO$). In this compound, copper exhibits a valency of +2.
- Chemical Equation:
$$2Cu(s) + O_2(g) \xrightarrow{\Delta} 2CuO(s)$$
(Reddish-brown) (Black)
Analysis of Incorrect Options:
- Copper(I) oxide ($Cu_2O$): This is a red oxide where copper has a valency of +1. It is typically formed under conditions of limited oxygen supply or through the reduction of Copper(II) oxide, not by simply heating copper in open air.
- Copper sulphide: This would require the presence of sulphur or hydrogen sulphide gas, not just air (oxygen).
- Copper hydroxide: This forms in the presence of moisture or aqueous solutions, not through dry heating.
Key Takeaway:
Heating copper metal in the presence of oxygen causes oxidation, resulting in the formation of a black coating of Copper(II) oxide ($CuO$).