Statement I : Colour of nitrogen dioxide changes to colourless at low temperature. Statement I : At low temperature Nitrogen tetroxide (N204) is formed which is colourless.

Nitrogen dioxide (NO2) is a reddish-brown gas [2]. It exists in a temperature-dependent equilibrium with its dimer, dinitrogen tetroxide (N2O4) [1]. The dimerization reaction (2NO2 ⇌ N2O4) is exothermic, meaning the formation of N2O4 is favored at lower temperatures. While NO2 is colored due to its unpaired electron, N2O4 is a colorless gas or liquid [2]. Consequently, as the temperature decreases, the equilibrium shifts toward the formation of the colorless dimer, causing the brown color of the gas mixture to fade or disappear. Statement I is true because the color change occurs as a result of this chemical shift. Statement II is also true and provides the correct scientific explanation for Statement I by identifying the formation of the colorless N2O4 species at low temperatures.

Sources

1. [2] https://pubchem.ncbi.nlm.nih.gov/compound/Nitrogen-oxide-_N2O4
2. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 12: Major Crops and Cropping Patterns in India > Biotic: Living > p. 116