pBlock ElementsII 1 Question 14
14. Concentrated nitric acid upon long standing, turns yellow-brown due to the formation of
(2013 Main)
(a) $\mathrm{NO}$
(b) $\mathrm{NO} _{2}$
(c) $\mathrm{N} _{2} \mathrm{O}$
(d) $\mathrm{N} _{2} \mathrm{O} _{4}$
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Answer:
Correct Answer: 14. (b)
Solution: 14. $\mathrm{NO} _{2}$ is a brown coloured gas and imparts this colour to concentrated $\mathrm{HNO} _{3}$ during long standing.
$$ 4 \mathrm{HNO} _{3} \longrightarrow 2 \mathrm{H} _{2} \mathrm{O}+2 \mathrm{NO} _{2}+3 \mathrm{O} _{2} $$
