Question

The $d$-electron configurations of $Cr ^{2+}, Mn^{2+}, Fe^{2+}$ and $Co ^{2+}$ are $d^{4}, d^{5}, d^{6}$ and $d^{7}$ respectively. Which one of the following will exhibit the lowest paramagnetic behaviour? (Atomic no. $Cr =24, Mn=25, Fe=26, Co=27$ ).

• A. $\left[ Co \left( H _{2} O \right)_{6}\right]^{2+}$
• B. $\left[ Cr \left( H _{2} O \right)_{6}\right]^{2+}$
• C. $\left[ Mn \left( H _{2} O \right)_{6}\right]^{2+}$
• D. $\left[ Fe \left( H _{2} O \right)_{6}\right]^{2-}$

Answer 1

Answer: (A)

$\therefore $ Since $Co ^{2+}$ has lowest no. of unpaired electrons hence lowest paramagnetic behaviour is shown by $\left[ Co \left( H _{2} O \right)_{6}\right]^{2+}$