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

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?

53 Explain why, an aqueous solution of sodium chloride is not used for the electrolytic extraction of sodium metal. 54 How are metals refined by the electrolytic process? Describe the electrolytic refining of copper with the help of a neat labelled diagram.