Identify the type of reactions in each of the following reactions:
$(i)$ $CaCO_{3} \xrightarrow{\text{Heat}} CaO + CO_{2}$
$(ii)$ $AgNO_{3}(aq) + NaCl(aq) \longrightarrow AgCl(s) \downarrow + NaNO_{3}(aq)$

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

State the kind of chemical reactions in the following examples:
$(a)$ Digestion of food in the stomach
$(b)$ Combustion of coal in air.

$A$ magnesium ribbon is burnt in oxygen to give a white compound $X$ accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen,it continues to burn and forms a compound $Y.$
$(a)$ Write the chemical formulae of $X$ and $Y.$
$(b)$ Write a balanced chemical equation,when $X$ is dissolved in water.

Grapes hanging on the plant do not ferment,but after being plucked from the plant,they can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

The coating formed on the metals such as iron, silver, and copper after corrosion will be: