(a) Why are `Mn^(2+)` compounds more stable than `Fe^(2+)` towards oxidation to their + 3 state?
(b) What are interstitial compounds ? Why are such compounds well-known for transition metals ?
(c) Write electronic configuration of `Pm^(3+)`.

Explanation

(a)` Mn^(2+) (3d^5 )-` exactly half filled and ectra stable and has high 3rd ionisation enthalpy `Fe^(2+ ) ( 3d ^6 )` can lose electron easily to get `Fe^(3+) (3d^5)` i.e., extra stable configuration
(b ) In such compounds the small atoms such as `h,c ` B,N etc occupy interstitial sites in their lattices eg. TiC `TiH_2 ,Fe_3H` steel etc such compounds Transition metals form such compounds because they can take up small atoms of C , h,B,N etc in their inerstitial sites in their lattices
(c ) ` Pm^(3-1) (61-3=58 e)`
`1s^2 2s^2 2p^6 3s^2 3d^6 3d^(10) 4s^2 4p^(10) 5s^2 5p^6 4f^4 "in" [Xe ]_54 4F^4 `