Question

the ground - state electron configuration of the element ____ is kr5s^14d^5.
o mn
o tc
o mo
o cr
o nb

Explanation:

1. Recall the electron - configuration rules and the positions of elements in the periodic table. The [Ar] core has 18 electrons. The given configuration [Ar]5s¹4d⁵ has a total of 18 + 1+5 = 24 electrons for the part after the noble - gas core.
2. Manganese (Mn) has an atomic number of 25 and its electron configuration is [Ar]4s²3d⁵.
3. Technetium (Tc) has an atomic number of 43 and its electron configuration is [Kr]5s²4d⁵.
4. Molybdenum (Mo) has an atomic number of 42. Due to the stability of half - filled sub - shells, its electron configuration is [Kr]5s¹4d⁵.
5. Chromium (Cr) has an atomic number of 24 and its electron configuration is [Ar]4s¹3d⁵.
6. Niobium (Nb) has an atomic number of 41 and its electron configuration is [Kr]5s¹4d⁴.

Answer:

C. Mo