An aqueous pink solution of cobalt (II) chloride changes to deep blue on addition of excess of `HCl`. This is because ....... .

Options

A. `[Co(H_(2)O_(6)]^(2+)` is transformed into `[CoCl_(6)]^(4-)`
B. `[Co(H_(2)O)_(6)]^(2+)` is transformed into `[CoCl_(4)]^(2-)`
C. tetrahedral complexes have smaller crystal field splitting than octahedral complexes
D. Tetrahedral complexes have larger crystal field splitting than octahedral complex

Answer

B, C

Explanation

Aqueous pink solution of cobalt (II) chloride is due to electronic transition of electron from `t_(2g)` to `e_(g)` energy level of `[Co(H_(2)O)_(6)]^(2+)` complex. When excess of HCl is added to this solution
(i) `[Co(H_(2)O)_(6)]^(2+)` is transformed into `[CoCl_(4)]^(2-)`.
(ii) Tetrahedral complexes have smaler crystal field splitting than octahedral complexes because `Delta_(t)=4/9 Delta_(0)`
Hence , option (b) and (c) are correct choices.