The number of hydroxyl groups in pyrophosphoric acid is ......... .

The oxide which forms a dimer is

Pure $HNO_3$ is colorless. However,it turns slightly brown when exposed to light due to its decomposition into $.....$.

In the ring test of $NO_{3}^{-}$ ion,$Fe^{2+}$ ion reduces nitrate ion to nitric oxide,which combines with $Fe^{2+}_{(aq)}$ ion to form a brown complex. Write the reactions involved in the formation of the brown ring.

The oxide of nitrogen formed by thermal decomposition of $NH_4NO_3$ is

Which of the following elements forms $p\pi-p\pi$ bond with itself?