A three-row table appeared in 2021, 2022, 2023 and 2025, always with a transition metal and at least one ion.
Exactly what was asked, with schedule answers
Species
Configuration
Why it catches people
Sc (2021)
[Ar] 3d¹ 4s²
First transition metal: 4s fills before 3d.
Fe³⁺ (2021, 2025)
[Ar] 3d⁵
Remove 4s electrons first, not 3d.
V (2022)
[Ar] 3d³ 4s²
Straightforward, but write 4s after 3d in shorthand.
Ni²⁺ (2022)
[Ar] 3d⁸
Again the 4s pair goes first.
Cr³⁺ (2023)
[Ar] 3d³
Cr itself is an exception, but the 3+ ion is regular.
Cu (2025)
[Ar] 3d¹⁰ 4s¹
Exception: a full d sublevel is worth promoting a 4s electron for.
⚠
Ions: 4s comes off first
It fills first but it empties first too. Fe is [Ar] 3d⁶ 4s², so Fe³⁺ is [Ar] 3d⁵ — not [Ar] 3d³ 4s². This single rule was worth marks in three of the five years. ℹ
What 2024 did instead
Rather than writing configurations, it gave 3p⁶ and asked what the 3, the p and the 6 each represent: the energy level (shell), the sublevel shape, and the number of electrons in that sublevel. Know the vocabulary, not just the procedure. ✓
Not assessed in 2026
The 2026 assessment specification states that Hund’s rule and the stability of half-filled sublevels will not be assessed (nor resonance). You still need Cu and Cr as memorised exceptions, but you will not be asked to justify them.