The reaction:

BaCl₂ (aq) + H₂SO₄ (aq) ⟶ BaSO₄ (s) + 2HCl (aq) is

(i) displacement reaction

(ii) neutralisation reaction

(iii) decomposition reaction

(iv) double displacement reaction

Thermal decomposition of sodium carbonate will produce

(i) carbon dioxide

(ii) oxygen

(iii) sodium hydroxide

(iv) no other product

Complete the following statements.

(a) The chemical change involving iron and hydrochloric acid illustrates a …………… reaction.

(b) In the type of reaction called …………… two compounds exchange their positive and negative radicals.

(c) A catalyst either …………… or …………… the rate of a chemical change but itself remains …………… at the end of the reaction.

(d) On heating, hydrated copper sulphate changes its colour from …………… to ……………

When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical changes involved in the two cases.