When concentrated HCI is added to an aqueous solution of `CoCl_(2) ` . Its colour changes from reddish pink to deep blue . Which complex ion gives blue colour in this reaction ?

Options

A. `[CoCl_(4)]^(2-)`
B. `[CoCl_(6)]^(3-)`
C. `[CoCl_(6)]^(4-)`
D. `[Co(H_(2)O)_(6)]^(2+)`

Answer

A

Explanation

When concentrated HCI is added in an aqueous solution of `CoCl_(2) `, then it forms `[Co Cl_(4)]^(2-)` -complex
`underset( "pink colour complex") ([Co(H_(2)O)_(6)]^(2+))+4Cl^(-) to underset("Blue colour complex")([Co(Cl)_(4)]^(2-))+6H_(2) O`