In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of: (a) N a₄ [ F e ( C N )₆ ]
(b) F e₄ [ F e ( C N )₆ ]³
(c) F e₂ [ F e ( C N )₆ ]
(d) F e₃ [ F e ( C N )₆ ]₄