How does the electrical conductivity of copper alloys, brass and bronze, differ from that of pure copper ?

50 Explain why, when a copper object remains in damp air for a considerable time, a green coating is formed on its surface. What is this process known as? 51 How does the painting of an iron object prevent its rusting? 51 What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder. 52 Explain giving equation, what happens when:

(a) ZnC0₃ is heated in the absence of air?

(b) a mixture of Cu₂O and Cu₂S is heated?