Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper, the other being CuO or cupric oxide. This red-coloured solid is a component of some antifouling paints. The compound can appear either yellow or red, depending on the size of the particles. Copper(I) oxide is found as the reddish mineral cuprite.
Molar mass：143.09 g/mol
Melting point：1,232 °C (2,250 °F; 1,505 K)
Boiling point：1,800 °C (3,270 °F; 2,070 K)
Solubility in water：Insoluble
Solubility in acid：Soluble
Band gap：2.137 eV
Magnetic susceptibility (χ)：-20·10−6 cm3/mol
Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints. Rectifier diodes based on this material have been used industrially as early as 1924, long before silicon became the standard. Copper(I) oxide is also responsible for the pink color in a positive Benedict's test.