Why do fireflies glow at night?

Who discovered hydrogen gas?

$(a)$ Balance the chemical equation:
$Fe(s) + H_2O(g) \rightarrow Fe_3O_4(s) + H_2(g)$
$(b)$ Identify the type of reaction in the equation given below:
$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + NaCl(aq)$

Which of the following is(are) an endothermic process(es)?
$(i)$ Dilution of sulphuric acid
$(ii)$ Sublimation of dry ice
$(iii)$ Condensation of water vapours
$(iv)$ Evaporation of water

Which of the following gases is of brown colour?

When $Zn$ metal is treated with a dilute solution of a strong acid,a gas is evolved,which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.