The brown gas prepared by the action of concentrated nitric acid on copper is an equilibrium mixture of dinitrogen tetraoxide and nitrogen dioxide : `N_(2)O_(4(g))overset(Endothermic)(hArr)2NO_(2(g))`
Which one of the following changes would result in a darkening of the colour?

Options

A. Increase in pressure
B. Increase in temperature
C. Addition of a catalyst
D. Removal of dinitrogen tetraoxide by liquefaction

Explanation

`N_(2)O_(4(g))hArr2NO_(2(g))`, `(DeltaH=+ve)`
Brown colour is formed due to `NO_(2)` gas. Darkening of colour is possible, when more `NO_(2)` is formed. When temperature increases the equilibrium shifted to the right side and more `NO_(2)` is formed.