Determine the element of lowest atomic number that contains a half-filled d subshell in the ground state?

Answer is: chromium (Cr).

Chromium with atomic number 24, it means it has 24 protons and 24 electrons.

Electron configuration of chromim atom: ₂₄Cr 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹.

In chromium, half full d-sub level (3d) is more stable than a partially filled d sub-level (3d⁴), thai is why an electron from the 4s orbital goes to a 3d orbital.

the positions which points up in upward carbon and down in downward carbon are axial

and vice versa holds true for equatorial positions

so the correct answer with labelled diagram will be

d

explanation: