Question

Please explain the answers:

1. Which is the correct ground state electron configuration for the Cr³⁺ ion?

A. [Ar] 4s¹3d⁵

B. [Ar] 4s¹3d²

C. [Ar] 4s²3d¹

D. [Ar] 3d³

E. [Ar] 4d³

2. Choose the diamagnetic species.

A. Ga³⁺     B. Cr²⁺     C. N      D. I      E. None of the above species are diamagnetic.

Answer 1

electron configuration of Cr is
[Ar] 3d5 4s1 when 3 electrons removed from outer shell
we get Cr3+ ion
electron configuration of Cr3+ is
[Ar] 3d3

hence answer
D. [Ar] 3d3
.................

diamagnetic substances have all paired electrons.
if a substance have unpaired electrons it is paramagnetic
from electronic configuration we can make out whether they are paired'
or not.

A. Ga3+
electron configuration : [Ar] 3d10 , all orbitals are paired
hence diamagnetic
B. Cr2+   
electron configuration :[Ar] 3d4 : It has 4 unpaired electrons
in d orbital. Hence it is paramagnetic
C. N
[He] 2s2 2p3 : it has 3 unpaired electrons hence paramagnetic
D. I
[Kr] 4d10 5s2 5p5 : It has 5 unpaired electrons Hence paramagnetic

answer
A. Ga3+
...............A. Ga3+

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