Name the type of reaction for the following:
$(i)$ Vegetable matter changing into compost.
$(ii)$ Burning of natural gas.

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 sulphur dioxide.

Which one of the following is a chemical change? Give reason also.
$A$. Burning of wax
$B$. Melting of wax

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
$(i)$ It is an endothermic reaction
$(ii)$ It is an exothermic reaction
$(iii)$ The $pH$ of the resulting solution will be more than seven
$(iv)$ The $pH$ of the resulting solution will be less than seven

Write the balanced chemical equations for the following reactions:
$(a)$ Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.
$(b)$ Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride,water,and liberates carbon dioxide.
$(c)$ Copper sulphate on treatment with potassium iodide precipitates cuprous iodide $(Cu_2I_2)$,liberates iodine gas,and also forms potassium sulphate.

$(a)$ Give an example of a combination reaction which is exothermic.
$(b)$ Identify the oxidizing agent and reducing agent in the following reaction:
$H_{2}S + Cl_{2} \rightarrow 2HCl + S$
$(c)$ Name the phenomenon due to which the taste and smell of oily food changes when kept for a long time in the open. Suggest one method to prevent it.