Why is a combustion reaction considered an oxidation reaction?

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
$(a)$ Thermit reaction,iron $(III)$ oxide reacts with aluminium and gives molten iron and aluminium oxide.
$(b)$ Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
$(i)$ Displacement reaction
$(ii)$ Precipitation reaction
$(iii)$ Combination reaction
$(iv)$ Double displacement reaction

$A$ small amount of quicklime is added to water in a beaker.
$(a)$ Name and define the type of reaction that has taken place.
$(b)$ Write the balanced chemical equation for the above reaction. Write the chemical name of the product obtained.
$(c)$ State two observations that you will make in the reaction.

The smell and taste of food containing fats and oils change after some time. Why does this happen? Name the process. List two ways which help to slow down the above-mentioned process.

Complete the missing components/variables given as $x$ and $y$ in the following reactions:
$(a)$ $Zn(s) + H_2SO_4(aq) \longrightarrow ZnSO_4(x) + H_2(y)$
$(b)$ $CaCO_3(s) \xrightarrow{x} CaO(s) + CO_2(g)$