Question

Concentrated $HN{O}_3,$ upon long standing, turns yellow-brown due to the formation of
(IIT-JEE, 2012)

• A. NO
• B. $N{O}_2$
• C. $N_{2}O$
• D. $N_2{O}_4$

Answer 1

The correct option is B $N{O}_2$

$4HN{O}_3\to 2H_{2}O+4N{O}_2+O_2$
$N{O}_2$ remains dissolved in $HN{O}_3$ colouring it yellow or even red at higher temperature.