Which gas is useful for inhibiting bacterial growth?

An element $A$ is soft and can be cut with a knife. It is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following:

$(a)$ 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.
$Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$
$Fe(s) + ZnSO_4(aq) \rightarrow FeSO_4(aq) + Zn(s)$

Write chemical equations for the reactions taking place when:
$(i)$ iron is strongly heated in air.
$(ii)$ lead carbonate is calcined.
$(iii)$ chromium oxide $(Cr_{2}O_{3})$ is heated with aluminium powder.

Which of the following metals are obtained by electrolysis of their molten chlorides?
$(i) Na, (ii) Ca, (iii) Fe, (iv) Cu$

By which method/process is sulphur obtained from the earth's crust?