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

Solution

Chemistry ma’am · 4 steps

55 protons means caesium. Remove its one 6s electron first, then count every s subshell.

1. Identify the ion. 55 protons is caesium, Cs. A unipositive ion has lost one electron, so Cs⁺ has 55 - 1 = 54 electrons. That is the same count as xenon.
2. Which electron leaves. Neutral Cs is [Xe] 6s¹. The outermost 6s electron is the one removed, so Cs⁺ has the xenon configuration.

   Cs⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶

3. Count s electrons. Five s subshells are filled: 1s, 2s, 3s, 4s, 5s. Each holds 2 electrons, so 5 × 2 = 10.
4. So. Cs⁺ has 10 s-electrons, option (a).

The idea to keep. For a cation, first remove electrons from the outermost shell, then write the configuration. To count s-electrons, list every filled s subshell from 1s up and multiply by 2.

Answer from the NTA final answer key. Solution by PrepWiser.