Question

How sulphur dioxide can be recognised?
A.By characterizing its pungent smell of burning sulphur
B.By its ability to turn dichromate paper green
C.Ability to decolourize acidified $KMn{O_4}$ solution
D.All of the above

Answer 1

Sulphur dioxide ($S{O_2}$) is a toxic gas having the smell of burnt matchsticks. It is an acidic oxide. On reaction with water it yields an acidic solution. $S{O_2} + {H_2} O \to {H_2}C{O_3}$

Complete answer:
Sulphur dioxide can be recognised by considering the following reaction of sulfites ($SO_3^ {2 -}$) and thiosulphates (${S_2} O_3^ {2 -}$). Both are anions and on reaction with dilute acid yield sulphur dioxide.
${S_2} O_3^ {2 -} + 2{H^ +} \to S + {H_2} O + S{O_2}$
${S_2} O_3^ {2 -} + 2{H^ +} \to S + {H_2} O + S{O_2}$
It is a colourless gas having a pungent odour of burning sulphur. With the aid of a U-tube the gas may be passed through a dilute solution of potassium permanganate, acidified with dilute sulfuric acid. The purple colour of potassium permanganate discharges.
$S{O_2} + {H_2} O \to {H_2}C{O_3}$
Similarly, when sulphur dioxide gas is passed through an acidified solution of potassium dichromate, the orange colour turns green due to the formation of chromium (III) sulphate. However, the green colour is so pale that it almost appears colourless.
${K_2}C{r_2}{O_7} + {H_2}S{O_4} + 3S{O_2} \to {K_2}S{O_4} + C{r_2}{(S{O_4})_3} + {H_2}O$
Thus from all the above reactions, we can say that sulphur dioxide can be characterized by its smell like burning sulphur, its ability to turn acidified solution of potassium dichromate and discoloration of potassium permanganate.
So, option D is the correct answer here.

Note: Sulphur dioxide is an air pollutant which reacts with other air pollutants to form sulphate products which affect the health of humans. It is majorly produced due to the expansion of coal-based electricity generation and burning of fossil fuels.