Which of the statements about the reaction below are incorrect ?

$2 PbO _{( s )}+ C _{( s )} \longrightarrow 2 Pb _{( s )}+ CO _{2( g )}$

$(a)$ Lead is getting reduced.

$(b)$ Carbon dioxide is getting oxidised.

$(c)$ Carbon is getting oxidised.

$(d)$ Lead oxide is getting reduced.

Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?

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.

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Translate the following statements into chemical equations and then balance them.

$(a)$ Hydrogen gas combines with nitrogen to form ammonia.

$(b)$ Hydrogen sulphide gas burns in air to give water and sulpur dioxide.

$(c)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

$(d)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

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