Why is a combustion reaction considered an oxidation reaction?

Complete the following reaction:
$2 FeSO_{4} \xrightarrow{\text{Heat}} Fe_{2}O_{3} + \dots + \dots$

Which among the following changes are exothermic or endothermic in nature?
$(a)$ Decomposition of ferrous sulphate
$(b)$ Dilution of sulphuric acid
$(c)$ Dissolution of sodium hydroxide in water
$(d)$ Dissolution of ammonium chloride in water

Complete the missing components/variables given as $x$ and $y$ in the following reactions:
$(a)$ $Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(x) + 2KNO_3(y)$
$(b)$ $Cu(s) + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + x(s)$

$A$ dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?

Write the chemical equation of the reaction with an example in which a change in colour takes place.