Question

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

• A. 8
• B. 12
• C. 9
• D. 10

Hint:

To count s-electrons, include all electrons in the s-subshells up to the element’s configuration.

Answer 1

The Correct Option is D

The element with 55 protons is cesium (Cs), and its atomic number is Z = 55. The electronic configuration of neutral Cs is:
\(Cs : [Xe] 6s ^1\)
For the unipositive ion Cs+, it loses the single 6s electron, and the configuration becomes:
\(Cs^+: [Xe]\)
Now count the total number of s-electrons in\( Cs^+:\)
• \(1s^2, 2s^2, 3s^2, 4s^2, 5s^2\) contribute \(2 × 5 = 10\) s-electrons.
Thus, the number of s-electrons is 10.