While preparing crystals of Mohr's salt, dil \( \mathrm{H_2SO_4} \) is added to a mixture of ferrous sulphate and ammonium sulphate, before dissolving this mixture in water, dil \( \mathrm{H_2SO_4} \) is added here to:
prevent the hydrolysis of ferrous sulphate
increase the rate of formation of crystals
prevent the hydrolysis of ammonium sulphate
make the medium strongly acidic