What is used as a catalyst in the production of sulfuric acid by the contact process?

Which among the following are physical or chemical changes?
$(a)$ Evaporation of petrol
$(b)$ Burning of Liquefied Petroleum Gas $(LPG)$
$(c)$ Heating of an iron rod to red hot
$(d)$ Curdling of milk
$(e)$ Sublimation of solid ammonium chloride

Which of the following gases is used as a preservative in fruit juices and jams?

Give reasons for the following:
$(i)$ Moist air and acidic gases are not good for some metals.
$(ii)$ Chips manufacturers usually flush bags of chips with nitrogen gas.

$NH_{3}$ is used in the preparation of nitric acid by $.....$ process.

Which method is used to collect $H_2$ gas in a gas jar in the laboratory?