Mixing of an aqueous salt solution containing nitrate ion with ferrous ion followed by gentle addition of conc. sulphuric acid from the sides of the test tube results in brown coloration at the interface. This is due to

A

interaction of ferrous ion with nitric oxide

B

interaction between the resulting nascent oxygen, ferrous ion and nitrate ion

C

formation of ferrous ion and nitrogen dioxide

D

complex formation between ferrous ion and nitrate ion