Electrons are filled into atomic orbitals in the increasing order of orbital energy level according to ?

Answer

a,c,d

Explanation

a,c,d are false but (b) is true,
(a). `Cr^(2+)implies3d^(4)4s^0`

4 unpaired electrons Magnetic moment`=sqrt(n(n+2))=sqrt(4(4+2))=sqrt(24)`
`Co^(3+)implies3d^64s^0`
4 unpaired electrons `=sqrt(4(4+2))=sqrt(24)`
(b) `Fe+e^(ɵ)overset(Delta_(eg)H^(ɵ))toFe^(ɵ)`
`Fe^(ɵ)overset(IE)toFe^(ɵ)+e^(ɵ)`
So ionisation energy of `Fe^(ɵ)` is equal `Delta_(eg)H^(ɵ)` of `Fe`.
(c) Pb have more ionisation potential than Sn due to poor shielding of 4f-orbital.
(d). There is a large jump in `IE_1toIE_2toIE_3`
but there is small jump in `IE_4toIE_5`. Hence number of valence electrons in given element is 3. Thus, from data of IE thus element corresponds to 13 group.