How many unpaired electrons are present in \(Ni^{2+}\)? (Atomic number of Ni = 28)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2
Unpaired electrons are counted from the d-electron configuration of the ion, filling the five 3d orbitals singly first and then pairing.
Oxidation state of Ni: the ion carries a charge of 2+, so Ni is in the +2 state.
Configuration: Ni (Z = 28) is [Ar]3d84s2; losing the two 4s electrons gives \( \ce{Ni^2+} \): [Ar]3d8.
Unpaired electrons: 8 electrons in five 3d orbitals give three pairs and two single electrons, so \( \ce{Ni^2+} \) has 2 unpaired electrons.
NCERT (2026-27 edition):
Table 4.7: Calculated and Observed Magnetic Moments (BM)
