Answer :
Answer is D - Argon atom
Potassium has atomic number as 19. Hence, number of protons = 19
If the atom is neutral,
number of protons = number of electrons = 19
Hence, the electron configuration of potassium (K) is
1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Potassium ion is formed by losing an electron. Then the number of electrons = 19 - 1 = 18
Electron configuration of K⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶.
This is same as the electron configuration of Ar which has 18 electrons.