Nitric acid: oxidation-reduction reactions
Decomposition
Concentrated nitric acid..
..is heated.
A brown gas is released: NO2
An incandescent piece of wood is introduced.
The wood takes fire: O2 was also released.
Concentrated nitric acid..
$4HNO_3$ $\longrightarrow$ $4NO_2$ $+$ $O_2$ $+$ $2H_2O$
