The number of s-electrons present in an ion with 55 protons in its unipositive state is:

Number of s-Electrons in Cs⁺ Ion | JEE Main PYQ | Structure of Atom

Q. The number of s-electrons present in an ion with 55 protons in its unipositive state is:

(A) 10

(B) 9

(C) 12

(D) 8

Correct Answer: 10

Explanation

Atomic number 55 corresponds to Cesium (Cs).

Electronic configuration of Cs:

1s² 2s² 3s² 4s² 5s² 6s¹

In unipositive state (Cs⁺), one electron is removed from 6s orbital.

So configuration of Cs⁺ becomes:

1s² 2s² 3s² 4s² 5s²

Total s-electrons:

1s² + 2s² + 3s² + 4s² + 5s² = 2 + 2 + 2 + 2 + 2 = 10

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