What type of chemical reaction takes place when i) limestone is heated?

ii) a magnesium ribbon is burnt in air?

(i) When limestone is heated the category of chemical reraction which takes place is decomposition reaction as during this reaction the limestone decomposes to form Calcium oxide with the liberation of carbon dioxide according to the following equation : -

CaCO₃→ CaO + CO₂↑ ( Reaction is taking place when heat is provided to limestone)

(ii) When a magnesium ribbon is burnt in air the category of chemical reaction which takes place is Combination reaction. During the reaction when we burn magnesium in the presence of air Magnesium combines with oxygen from the air to form a single product namely magnesium oxide as the product. Hence, it is a combination reaction and follows the following equation: -

2Mg + O₂ → 2MgO