Which of the following particles has the same electron configuration as a potassium ion (K^+)?

• A. Cl^-
• B. Ar
• C. Na^+
• D. Ca^2+

Answer: (B)

Verified step by step guidance

1. Step 1: Identify the electron configuration of a neutral potassium (K) atom. Potassium has an atomic number of 19, so its electron configuration is \$1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$.
2. Step 2: Determine the electron configuration of the potassium ion \(K^+\). Since it has lost one electron, remove one electron from the outermost shell (4s orbital), resulting in \$1s^2 2s^2 2p^6 3s^2 3p^6$.
3. Step 3: Recognize that the electron configuration \$1s^2 2s^2 2p^6 3s^2 3p^6$ corresponds to the electron configuration of argon (Ar), which has 18 electrons.
4. Step 4: Compare the electron configurations of the other ions: \(Cl^-\) has gained one electron (18 electrons), \(Na^+\) has lost one electron (10 electrons), and \(Ca^{2+}\) has lost two electrons (18 electrons).
5. Step 5: Conclude that the particles with the same electron configuration as \(K^+\) are those with 18 electrons, which includes \(Ar\), \(Cl^-\), and \(Ca^{2+}\). Among the given options, \(Ar\) is the correct answer as it is a neutral atom with the same electron configuration.