Which method is used for the refining of metals having low melting points?

Generally, metals react with acids to produce salt and hydrogen gas. Which of the following acids does not produce hydrogen gas when reacting with most metals (except $Mn$ and $Mg$)?

Which one of the following metals does not react with cold as well as hot water?

Which method is used for the refining of copper metal?

Name two metals which are purified by electrolytic refining. Mention the anode,cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?

$(a)$ An ore on heating in air gives sulphur dioxide gas. Name the method in each metallurgical step that will be required to extract this metal from its ore.
$(b)$ State which of the following reactions will take place or not,giving a suitable reason for each.
$Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$
$Fe(s) + ZnSO_4(aq) \rightarrow FeSO_4(aq) + Zn(s)$