To determine which electron configuration represents a transition element, we first need to understand what qualifies an element as a transition element. A transition element is generally defined as one that has an incomplete d sub-level or can form cations with an incomplete d sub-level.
Let’s examine each of the given electron configurations:
(A) [tex]\(1s^2 2s^2 2p^5\)[/tex]
This configuration corresponds to a total of 9 electrons (1 + 1 + 4 + 2 + 1), which makes it the configuration of fluorine. Fluorine is not a transition element as it does not have a d sub-level.
(B) [tex]\([Ne] 3s^2\)[/tex]
This configuration corresponds to 10 electrons from neon plus 2 from the [tex]\(3s^2\)[/tex] subshell, giving a total of 12 electrons. This is the electron configuration of magnesium. Magnesium is an alkaline earth metal, not a transition element, as it does not have an incomplete d sub-level.
(C) [tex]\([Ar] 3d^5 4s^2\)[/tex]
This configuration adds the electrons of argon (18 electrons) to the 3d and 4s subshells. This configuration corresponds to 25 electrons, which belongs to manganese. Manganese has a partially filled 3d sub-level ([tex]\(3d^5\)[/tex]), making it a transition element. Therefore, this configuration represents a transition element.
(D) [tex]\([Ar] 3d^{10} 4s^2 4p^6\)[/tex]
This configuration corresponds to the electrons of argon (18 electrons) plus 10 from the 3d subshell, 2 from the 4s subshell, and 6 from the 4p subshell, amounting to a total of 36 electrons, the configuration of krypton, which is a noble gas and hence not a transition element.
Among the given options, only choice (C) [tex]\([Ar] 3d^5 4s^2\)[/tex] represents a transition element due to its partially filled 3d sub-level.
Therefore, the correct answer is (C).
