Final answer:
The species with the highest effective nuclear charge (Zeff) among Cl, Cl-, K, and K+ is K+. This is due to the loss of an electron when K becomes K+, reducing electron-electron repulsion and resulting in electrons experiencing a stronger attraction from the nucleus.
Step-by-step explanation:
The question asks which species has the highest effective nuclear charge, or Zeff. Effective nuclear charge refers to the net positive charge experienced by electrons in the valence shell of an atom or ion. This charge takes into account the repulsion from other electrons and closer shells that shield the nucleus's effective charge.
For Cl, Cl-, K, and K+, the highest Zeff would be for K+. This is because when the neutral potassium atom (K) loses an electron to become K+, it has one fewer electron repelling each other and creating a shield. As a result, the remaining electrons experience a stronger attraction from the nucleus.
Therefore, K+ has a greater Zeff than neutral K. Cl has an added electron compared to Cl-, which increases electron-electron repulsion and results thus decreasing Zeff compared to its neutral form. Therefore, Cl- does not have the highest Zeff.
Since Cl has an additional proton compared to K or K+, one might think it could have a higher Zeff, but we must consider the electron configuration and the electrons' shielding effect as well. Cl and Cl- have more electrons so increased shielding results in a lower Zeff as compared to K+.
Electron affinity and ionization energy are relevant to the processes of gaining and losing electrons but do not directly determine the Zeff. Thus, the correct option is C) K+; it has lost an electron.