What is mixed with natural rubber to obtain vulcanized rubber?

Non-metals form two types of oxides. Choose these two types from the following oxides:
$SO_2, NO_2, CO, H_2O, N_2O$

$(a)$ Carbon cannot be used as a reducing agent to obtain $Mg$ from $MgO$. Why?
$(b)$ How is sodium obtained from molten sodium chloride? Give the equations of the reactions.
$(c)$ How is copper obtained from its sulphide ore? Give the equations of the reactions.

Give reasons for the following:
$(a)$ We can store copper sulphate solution in a silver vessel but not silver nitrate solution in a copper vessel.
$(b)$ The reaction of zinc with dilute nitric acid does not produce hydrogen gas.
$(c)$ Food cans are coated with tin rather than zinc.

What are the components of bronze?

$(a)$ Write the chemical name of the coating that forms on silver and copper articles when these are left exposed to moist air.
$(b)$ Explain what is galvanisation? What purpose is served by it?
$(c)$ Define an alloy. How are alloys prepared? How do the properties of iron change when:
$(i)$ small quantity of carbon,
$(ii)$ nickel and chromium are mixed with it.