Cobalt chloride when dissolved in water forms pink colored complex $\underline{\mathrm{X}}$ which has
octahedral geometry. This solution on treating with conc $\mathrm{HCl}$ forms deep blue complex, $\underline{\mathrm{Y}}$ which has a $\underline{\mathrm{Z}}$ geometry. $\mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$, respectively, are
$\mathrm{X}=\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}, \mathrm{Y}=\left[\mathrm{CoCl}_{4}\right]^{2-}, \mathrm{Z}=$ Tetrahedral
$\mathrm{X}=\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}, \mathrm{Y}=\left[\mathrm{CoCl}_{6}\right]^{3-}, \mathrm{Z}=$ Octahedral
$\mathrm{X}=\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\right]^{+}, \mathrm{Y}=\left[\mathrm{CoCl}_{4}\right]^{2-}, \mathrm{Z}=$ Tetrahedral
$\mathrm{X}=\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}, \mathrm{Y}=\left[\mathrm{CoCl}_{6}\right]^{3-}, \mathrm{Z}=$ Octahedral
