Which of the following complex will show largest splitting of d-orbitals?

Which of the following are the example of double salt?

A. $$\mathrm{FeSO}_{4} \cdot\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}$$

B. $$\mathrm{CuSO}_{4}\cdot 4 \mathrm{NH}_{3} \cdot \mathrm{H}_{2} \mathrm{O}$$

C. $$\mathrm{K}_{2} \mathrm{SO}_{4} \cdot \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3} \cdot 24 \mathrm{H}_{2} \mathrm{O}$$

D. $$\mathrm{Fe}(\mathrm{CN})_{2}\cdot4 \mathrm{KCN}$$

Choose the correct answer :

A solution of $$\mathrm{FeCl_3}$$ when treated with $$\mathrm{K_4[Fe(CN)_6]}$$ gives a prussium blue precipitate due to the formation of :

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