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

When cobalt chloride (CoCl$$_2$$) is dissolved in water:

The water molecules coordinate with Co$$^{2+}$$ to form the pink-colored hexaaquacobalt(II) complex:

$$ X = [Co(H_2O)_6]^{2+} \quad \text{(Octahedral geometry)} $$

When this solution is treated with concentrated HCl, the water ligands are replaced by chloride ions to form the deep blue tetrachlorocobaltate(II) complex:

$$ [Co(H_2O)_6]^{2+} + 4Cl^- \rightarrow [CoCl_4]^{2-} + 6H_2O $$

$$ Y = [CoCl_4]^{2-} \quad \text{(Tetrahedral geometry)} $$

Therefore: X = $$[Co(H_2O)_6]^{2+}$$, Y = $$[CoCl_4]^{2-}$$, Z = Tetrahedral.