Aqueous $$\mathrm{CuSO}_4$$ changes its colour from sky blue to deep blue on addition of $$\mathrm{NH}_3$$ because

Which of the following complex show optical isomerism?

(i) $$c i s-\left[\mathrm{COCl}(\mathrm{en})_2\left(\mathrm{NH}_3\right)\right]^{2+}$$

(ii) $$cis-\left[\mathrm{CrCl}_2(\mathrm{ox})_2\right]^{3-}$$

(iii) $$cis-[ \left.\mathrm{CO}(\mathrm{en})_2 \mathrm{Cl}_2\right] \mathrm{Cl}$$

(iv) $$cis- \left[\mathrm{CO}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right]^{+}$$

Mohr's salt has the formula

Identify the correct IUPAC name of $$[\mathrm{CoCl}_2(\mathrm{NO}_2)(\mathrm{NH}_3)_3]$$