Why do we apply paint on iron articles?

Identify the substances that are oxidised and the substances that are reduced in the following reactions.
$(i)$ $4Na(s) + O_2(g) \rightarrow 2Na_2O(s)$
$(ii)$ $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)$

Write a balanced chemical equation with state symbols for the following reactions.
$(i)$ Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
$(ii)$ Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Why is the amount of gas collected in one of the test tubes in the image double the amount collected in the other? Name this gas.

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Write the balanced chemical equations for the following reactions.
$(a)$ Calcium hydroxide $+$ Carbon dioxide $\rightarrow$ Calcium carbonate $+$ Water
$(b)$ Zinc $+$ Silver nitrate $\rightarrow$ Zinc nitrate $+$ Silver
$(c)$ Aluminium $+$ Copper chloride $\rightarrow$ Aluminium chloride $+$ Copper
$(d)$ Barium chloride $+$ Potassium sulphate $\rightarrow$ Barium sulphate $+$ Potassium chloride