When aqueous $Co X^{2 +}$ is treated with excess solid $NH X_{4} SCN$ and shaken with amyl alcohol, the organic layer turns blue. The geometry of the blue species $[Co (NCS) X_{4}] X^{2 -}$ is

Answer: D

Co X^{2 +}

(

d^{7}

) with the weak-field, bulky thiocyanate ligand forms the tetrahedral

[Co (NCS) X_{4}] X^{2 -}

, which is blue and extracted into the organic layer. The aqua ion is pink and octahedral.