The correct order of first ( iH1) and second ( iH2) ionisation enthalpy values of Cr and Mn are : Choose the correct answer from the options given below :
- A and B only
- B and C only
- A and D only
- C and D only
Answer
(2) B and C only
Solution
Cr: [Ar]3d54s1; Mn: [Ar]3d54s2
iH1: Mn loses an electron from a filled 4s subshell with a stable 3d5 core ⇒ Mn (717 kJ mol-1) > Cr (653 kJ mol-1) ⇒ C is correct
iH2: Cr+ is 3d5 (half-filled, stable) while Mn+ is 3d54s1 ⇒ Cr (1592 kJ mol-1) > Mn (1509 kJ mol-1) ⇒ B is correct
∴ B and C only
Answer: (2)