Which of the following are exothermic processes?
$(i)$ Reaction of water with quicklime
$(ii)$ Dilution of an acid
$(iii)$ Evaporation of water
$(iv)$ Sublimation of camphor (crystals)

Balance the following chemical equations and identify the type of chemical reaction.
$(a)$ $Mg(s) + Cl_2(g) \to MgCl_2(s)$
$(b)$ $HgO(s) \xrightarrow{\text{Heat}} Hg(l) + O_2(g)$
$(c)$ $Na(s) + S(s) \xrightarrow{\text{Fuse}} Na_2S(s)$

Translate the following statements into chemical equations and then balance them.
$(a)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
$(b)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Which one is a chemical change: Electrolysis of water or Sodium chloride exposed to sunlight?

Which is the reducing agent in the following reaction?
$MnO_{2}(s) + 4HCl(aq) \longrightarrow MnCl_{2}(s) + 2H_{2}O(l) + Cl_{2}(g)$

$A$ student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings.