# Consider the ground state of Cr atom (Z = 24). The numbers of electrons with the azimuthal quantum numbers,  = 1 and 2 are, respectively:        (A)    16 and 5        (B)    12 and 5        (C)    16 and 4        (D)    12 and 4

Grade:upto college level

## 3 Answers

Aditi Chauhan
askIITians Faculty 396 Points
9 years ago

(B)

Sol.    = 1 p and  = 2 for d.

Now Cr has configuration

1s2 2s2 2p6 3s2 3p6 3d5 4s1

Hence there are 12, p-electrons and 5, d-electrons

Aviral singh
15 Points
4 years ago
Answer is 2(second option)because the correct electronic configuration  of Cr is:1s2 1s2, 2s2, 2 2p6 p6, 3s2, 3p6, 4s1, 3d5.
Usually we consider the electronic configuration  as: 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d4.
But this is wrong because 3d4 wats to achieve half stability.So it takes 1 electron from 4s2.Now 4s2 becomes 4s1 and 3d4 becomes 3d5 and attains half stability.
Now, for l=1(azimuthal quantum number)subshell is p....
And here for subshell p, number of electrons(I.e.2p6 and 3p6)total no. Of electrons=12.
For l=2(azimuthal quantum number),subshell is d....and total number of electrons for subshell d(I.e.4d5)total no. Of electrons=5....
So the combination(12,5)....i.e.option(b) is correct.

Thank you🙏

Kushagra Madhukar
askIITians Faculty 628 Points
3 years ago
Dear student,
Please find the solution to your problem.

Cr has electronic configuration
1s2 2s2 2p6 3s2 3p6 3d5 4s1
Hence there are 12, p-electrons and 5, d-electrons

Thanks and regards,
Kushagra

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