The existence of two different colored complexes of $[Co(NH_3)_4Cl_2]^+$ is due to which of the following?

For a tetrahedral complex $[MCl_{4}]^{2-}$,the spin-only magnetic moment is $3.83 \ BM$. The element $M$ is

$[Co(en)_3]^{3+}$ ion is expected to show

Among the complex ions,$[Co(en)_2Cl_2]^{+}$,$[CrCl_2(C_2O_4)_2]^{3-}$,$[Fe(H_2O)_4(OH)_2]^{+}$,$[Fe(NH_3)_2(CN)_4]^{-}$,$[Co(en)_2(NH_3)Cl]^{2+}$ and $[Co(NH_3)_4(H_2O)Cl]^{2+}$,the number of complex ion$(s)$ that show$(s)$ cis-trans isomerism is

Which of the following is not correctly matched?

Which ion has the least value of theoretical magnetic moment?