For the four successive transition elements (Cr, Mn, Fe and Co), the stability of +2 oxidation state will be there in which of the following order? (At. no. Cr =24, Mn =25, Fe =26, Co =27 )

Step-by-step solution

This can be understood on the basis of E^ values for M²⁺ / M . array lrrcr E % V & Cr & Mn & Fe & Co M²⁺ / M & -0.90 & -1.18 & -0.44 & -0.28 array E^ value for Mn is more negative than expected from general trend due to extra stability of half-filled Mn ²⁺ ion. Thus the correct order should be, Mn > Cr > Fe > CO an examination of E^ values for redox couple M³⁺ / M²⁺ shows that Cr ²⁺ is strong reducing agent (E_ M³⁺ ^ / M²⁺=0.41 ~V ) and liberates H ₂ from dilute acids. 2 Cr ²⁺(a q)+2 H ⁺(a q) 2 Cr ³⁺(a q)+ H ₂ (g)