COMEDK2024Morning ShiftChemistryd and f Block ElementsActual
Arrange the following ions in the increasing order of their H_ ( hydration ) values. Cr ²⁺, Co ²⁺, Mn ²⁺, Ni ²⁺
Options
- ACr ²⁺< Mn ²⁺< Co ²⁺< Ni ²⁺
- BCo ²⁺< Ni ²⁺< Cr ²⁺< Mn ²⁺
- CMn ²⁺< Cr ²⁺< Co ²⁺< Ni ²⁺
- DNi ²⁺< Co ²⁺< Mn ²⁺< Cr ²⁺
Correct answer
C. Mn ²⁺< Cr ²⁺< Co ²⁺< Ni ²⁺
Step-by-step solution
The enthalpy of hydration ( H_ hydration ) for transition metal ions is primarily determined by the charge-to-size ratio, which is inversely proportional to the ionic radius. As the atomic number increases across the 3d series for ions of the same charge ( +2 ), the effective nuclear charge increases, leading to a decrease in ionic radius. The ionic radii for the given M²⁺ ions follow the order: Mn ²⁺ > Cr ²⁺ > Co ²⁺ > Ni ²⁺ . Since H_ hydration is directly proportional to the charge density (which is inversely pro