Cobalt chloride when dissolved in water forms pink colored complex X which has octahedral geometry. This solution on treating with cone HCl forms deep blue complex, Y which has a Z geometry. X , Y and Z , respectively, are

Step-by-step solution

Cobalt chloride when dissolved in water forms pink coloured is Co H 2 O 6 Cl 2 . This is due to the electronic transition of an electron from t 2 g to e g energy level of Co H 2 O 6 2 + complex. When excess of HCl is added to the solution Co H 2 O 6 2 + is transformed into deep blue colour complex [ CoCl 4 ] 2 − . △ t =   4 9   △ o △ t   <   △ o Tetrahedral complexes have smaller crystal field splitting than octahedral complexes. CoCl 2 + 6 H 2 O ⟶ Co H 2