Which among the following statement$(s)$ is(are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to:
$(i)$ The formation of silver by decomposition of silver chloride
$(ii)$ Sublimation of silver chloride
$(iii)$ Decomposition of chlorine gas from silver chloride
$(iv)$ Oxidation of silver chloride

Write a balanced chemical equation for the reaction in which phosphorus burns in chlorine to form phosphorus pentachloride.

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

$A$ 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.

The following reaction is used for the preparation of oxygen gas in the laboratory:
$2KClO_{3(s)} \xrightarrow[Catalyst]{Heat} 2KCl_{(s)} + 3O_{2(g)}$
Which of the following statement$(s)$ is(are) correct about the reaction?

State what happens when:
$(a)$ Gypsum is heated at $373 \, K$.
Also,write the chemical equation for the reaction.