The complex that shows Facial - Meridional isomerism is

Increasing order of magnetic moments of $I. [Fe(CN)_6]^{4-}$,$II. [Fe(CN)_6]^{3-}$,$III. [Cr(NH_3)_6]^{3+}$,$IV. [Ni(H_2O)_4]^{2+}$ is

The value of $1$ Bohr magneton $(\mu_B)$ is equal to ......... $A \cdot m^2$.

Which of the following is not correctly matched?

Which of the following complex species is not expected to exhibit optical isomerism?

The octahedral complex $[Co(NH_3)_5SO_4]Cl$ exists in two isomeric forms $X$ and $Y$. Isomer $X$ reacts with $AgNO_3$ to give a white precipitate,but does not react with $BaCl_2$. Isomer $Y$ gives a white precipitate with $BaCl_2$ but does not react with $AgNO_3$. Isomers $X$ and $Y$ are $.....$