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

Why do we store silver chloride in dark-coloured bottles?

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

The following reaction is an example of a:
$4 NH_{3}(g) + 5 O_{2}(g) \rightarrow 4 NO(g) + 6 H_{2}O(g)$
$(i)$ Displacement reaction
$(ii)$ Combination reaction
$(iii)$ Redox reaction
$(iv)$ Neutralisation reaction

$A$ reddish-brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish, its colour turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on the above information, answer the following questions:
$(i)$ Name the metal and the black coloured substance formed.
$(ii)$ Write balanced chemical equations for both the reactions.

Write two observations for the following chemical reaction:
$(a)$ Dilute sulphuric acid is poured over zinc granules.