Which of t he following is False?

Options

A. `Cr_(g)^(2+)` ion has greater magnetic moment as compared to `Co_(g)^(3+)`.
B. The magnitude of ionisation potential of iron anion (monoanion) would be equal to electron gain enthalpy of iron.
C. Lanthanoids contraction is cause of lower IE of Pb than Sn.
D. If successive ionisation energy are 332,738,849,4080,4958 (in `(kJ)/(mol)`). Then this element can be of 15th group.

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.