A white crystalline solid 'A' on boiling with caustic soda solution gives a gas 'B', which on passing through an alkaline solution of potassium tetraiodomercurate (II) solution gives a brown ppt. The substance 'A' on heating evolves a neutral gas 'C', which is inert at room temperature and reactive in presence of catalyst and does not give brown fumes with nitric oxide.
The gas 'C' is:
a. N2O
b. O2
c. NO
d. N2