Which method/process is used to prepare sulphuric acid?

$(a)$ When calcium metal is added to water,the gas evolved does not catch fire,but the same gas evolved on adding potassium metal to water catches fire. Explain why?
$(b)$ Name a metal for each case:
$(i)$ It displaces hydrogen gas from nitric acid.
$(ii)$ It does not react with any physical state of water.
$(iii)$ It does not react with cold as well as hot water but reacts with steam.

Which of the following can undergo a chemical reaction?

Which of the following gases acts as a mild bleaching agent?

Explain the following:
$(a)$ $NaCl$ is not a conductor of electricity in solid state,whereas it does conduct electricity in aqueous solution as well as in molten state.
$(b)$ Iron articles are galvanised.
$(c)$ Metals like $Na, K, Ca$ and $Mg$ are never found in their free state in nature.

What is the name of the apparatus used for the electrolysis of pure water?