Question

A white precipitate insoluble in $$HN{O}_3$$ is formed when the aqueous solution of x in NaOH is treated with barium chloride and bromine water. So x is :
A. $S{O}_3$
B. $S{O}_2$
C. $C{O}_2$
D. None of the above

Answer 1

Hint: It is a colourless, pungent smelling gas and is highly soluble in water. It is used to make sulphurous acid ($H_{2}S{O}_3$), sulphuric acid($H_{2}S{O}_4$). It behaves as a reducing agent when moist.

Complete-step- by- step answer:
When the aqueous solution of $S{O}_2$ ​in $NaOH$ ​when treated with barium chloride and bromine water, a white precipitate is formed which is insoluble in conc.$HN{O}_3$.
We can see in the reaction that $S{O}_2$ readily reacts with sodium hydroxide solution to form sodium sulfite.
     $$S{O}_2+2NaOH\to N{a}_{2}S{O}_3+H_{2}O$$

The sodium sulphite is then treated with barium chloride to form barium sulfite $BaS{O}_3$
     $$N{a}_{2}S{O}_3+BaC{l}_2\to BaS{O}_3+2NaCl$$

Now the barium sulfite is lastly treated with bromine water . the bromine water contains nascent oxygen $\left[O\right]$
     $$B{r}_2+H_{2}O\to 2HBr+\left[O\right]$$
This nascent oxygen oxidises the barium sulfite to give a white precipitate which is insoluble in conc.$HN{O}_3$ it is barium sulphate $BaS{O}_4$.
     $$BaS{O}_3+\left[O\right]\to BaS{O}_4$$
Sulphur (S) is a p- block element of group 16. Its main oxides are $S{O}_2$ and $S{O}_3$.
Sulphur dioxide is a colourless gas, we can easily identify it due its pungent smell. It has an angular shape and the bond length is the same. It forms a resonance hybrid of the two canonical forms.

Sulphur dioxide has many different uses such as refining petroleum and sugar, bleaching wool and silk and as an anti – chloral, preservative and disinfectant.
Therefore we can conclude that the answer is option B. $S{O}_2$.

Note: -In the question we are given an important reaction of sulphur dioxide with $NaOH$, its reaction with barium chloride and bromine water, it is also used to test the presence of$S{O}_2$.
Keep in mind the basic properties of a gas to determine its presence as for example sulphur dioxide is a colourless and pungent smelling gas.$$$$