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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3qa031

After a salt is treated with dilute $H X_{2} SO X_{4}$ , a colourless gas is collected. Which of the following tests distinguish $SO X_{2}$ (from a sulphite) from $CO X_{2}$ (from a carbonate)?

AMoist acidified $K X_{2} Cr X_{2} O X_{7}$ paper
BAcidified $KMnO X_{4}$ solution
CLime water
DAqueous iodine solution with starch

Answer: A, B, D

SO X_{2}

is a reducing gas. It turns orange dichromate green, decolourises purple permanganate and decolourises the iodine-starch blue colour (

SO X_{2} + I X_{2} + 2 H X_{2} O H X_{2} SO X_{4} + 2 HI

).

CO X_{2}

does none of these. Both gases turn lime water milky, so that test cannot distinguish them.

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