Concentrated `HNO_3`, upon long standing, turns yellow-brown due to the formation of

Concentrated nitric acid, upon long standing, turns yellow- brown due to the formation of

Concentrated nitric acid upon long standing turns yellowish-brown due to the formation of :

In the fourth group, white precipitate of Mn(OH)_(2) on heating with PbO_(2) and concentrated HNO_(3) gives red-violet (purple) colour due to the formation of: