KCET 2026 Chemistry Solved Paper

Concept:Spin-only magnetic moment depends on the number of unpaired electrons: $\mu = \sqrt{n(n+2)}$ BM.Explanation:Chromium has atomic number 24, so its configuration is $[\mathrm{Ar}]\,3d^5\,4s^1$.For $\mathrm{Cr}^{2+}$, two electrons are removed: first from $4s$, then one from $3d$.Thus, $\mathrm{Cr}^{2+} = [\mathrm{Ar}]\,3d^4$.According to Hund's rule, the four $3d$ electrons occupy separate orbitals, giving $n = 4$ unpaired electrons.Substituting into the formula:$\mu = \sqrt{4(4+2)} = \sqrt{24} = 4.90\,\mathrm{BM}$.Answer:$4.90\,\mathrm{BM}$, which is Option B.