Statement-I: Colour of nitrogen dioxide changes to colourless at low temperature.
Statement-II: At low temperature Nitrogen tetroxide (N₂O₄) is formed which is colourless.
[amp_mcq option1=”Both the statements are individually true and Statement II is the correct explanation of Statement I” option2=”Both the statements are individually true but Statement II is not the correct explanation of Statement I” option3=”Statement I is true but Statement II is false” option4=”Statement I is false but Statement II is true” correct=”option1″]
This question was previously asked in
UPSC NDA-1 – 2015
2NO₂(g) (reddish-brown) ⇌ N₂O₄(g) (colourless)
This dimerization reaction is exothermic (ΔH < 0). According to Le Chatelier's principle, decreasing the temperature shifts the equilibrium towards the exothermic reaction, favoring the formation of N₂O₄. As the temperature decreases, more NO₂ dimerizes into colourless N₂O₄, causing the colour of the gas mixture to fade to colourless. Statement II correctly identifies the formation of colourless N₂O₄ as the reason for the colour change.