JEE MainChemistryd and f Block Elements
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The standard reduction potential ( E^ ) for the Mn ³⁺/ Mn ²⁺ couple is much more positive than that for the Fe ³⁺/ Fe ²⁺ couple. Reason (R): The third ionization enthalpy of manganese is exceptionally high because removing an electron from the stable 3 d ⁵ configuration of Mn ²⁺ requires a large am
Options
- ABoth (A) and (R) are correct but (R) is NOT the correct explanation of (A)
- BBoth (A) and (R) are correct and (R) is the correct explanation of (A)
- C(A) is correct but (R) is not correct
- D(A) is not correct but (R) is correct
Correct answer
B. Both (A) and (R) are correct and (R) is the correct explanation of (A)
Step-by-step solution
The standard reduction potential E^ ( M ³⁺/ M ²⁺) depends on the hydration enthalpy and ionization enthalpies. For Mn , the transition from Mn ²⁺ ( 3 d ⁵ ) to Mn ³⁺ ( 3 d ⁴ ) involves breaking a highly stable half-filled d-subshell. This results in an exceptionally high third ionization enthalpy for Mn , making the oxidation of Mn ²⁺ difficult and the reduction of Mn ³⁺ highly favorable. Consequently, the E^ ( Mn ³⁺/ Mn ²⁺) value is very positive ( +1.57 V ). In contrast, for Fe , the transition from Fe ²⁺ ( 3 d ⁶