Which of the following gases can be used for the storage of a fresh sample of an oil for a long time?

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
$(i)$ Displacement reaction
$(ii)$ Precipitation reaction
$(iii)$ Combination reaction
$(iv)$ Double displacement reaction

Calcium oxide reacts vigorously with water to produce:

State the reason for the following:
$(a)$ Potato chips manufacturers usually flush bags of chips with nitrogen gas.
$(b)$ Iron articles lose their shine gradually.
$(c)$ Foods should be kept in airtight containers.

Can oxidation or reduction take place alone? Why or why not? What are such reactions called?

Explain the type of reaction represented by the following equation:
$(i) \ CuSO_{4} + 2NaOH \longrightarrow Cu(OH)_{2} + Na_{2}SO_{4}$