Let’s begin by examining the noble gas configuration for each element. Remember, we can use noble gas configuration to significantly shorten an element’s electron configuration by utilizing the elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons.
For Kr, it’s noble gas configuration would be [Kr]. This is because the Kr noble gas must be isoelectronic to itself, therefore producing the same configuration for both noble gas and electronic form.
For Zn, it’s noble gas configuration would be [Ar] 4s^2 3d^10, as Ar was the last noble gas prior to the Zn atom. Zn has exactly the right amount of electrons to fill the 3d sub level, so the configuration ends with 3d^10.
For Cd, it’s noble gas configuration would be [Kr] 5s^2 4d^10, as Kr was the last noble gas prior to the Cd atom. Cd has exactly the right amount of electrons to fill the 4d sub level, so the configuration ends with 4d^10.
For Cu, it’s noble gas configuration would be [Ar] 4s^2 3d^9, as Ar was the last noble gas prior to the Cu atom. Cu can only fill the 3d sub level with 9 electrons, so the configuration ends at 3d^9.
Therefore, the correct answer is B) Zinc!