What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder.

51 How does the painting of an iron object prevent its rusting? 51 How does the electrical conductivity of copper alloys, brass and bronze, differ from that of pure copper ? 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?

53 For the reduction of a metal oxide, suggest a reducing agent other than carbon.