Class 11 NEET Chemistry Classification Of Elements And Periodicity In Properties

Concept:Comparing atomic/ionic radii, IUPAC nomenclature rules, diagonal relationship in periodic table, and oxidation state with covalency in coordination complexes.Chemical Equation / Formula:Isoelectronic series: $\mathrm{Mg}^{2+}$ (10 e⁻, 12 p⁺), $\mathrm{Al}^{3+}$ (10 e⁻, 13 p⁺); atomic sizes: $\mathrm{Mg}$ > $\mathrm{Al}$ > $\mathrm{Mg}^{2+}$ > $\mathrm{Al}^{3+}$.Atomic number 107 corresponds to element with IUPAC temporary name "Unnilseptium" (symbol Uns).$\mathrm{Li}$ and $\mathrm{Mg}$ show diagonal relationship due to similar charge density.In $[\mathrm{AlCl}(\mathrm{H_2O})_5]^{2+}$, oxidation state of Al is +3 and covalency (coordination number) is 6.Explanation:Statement A is incorrect. Among $\mathrm{Mg}$, $\mathrm{Mg}^{2+}$, $\mathrm{Al}$, and $\mathrm{Al}^{3+}$, the largest species is $\mathrm{Mg}$ (neutral atom with larger atomic radius), and the smallest is $\mathrm{Al}^{3+}$ (highest nuclear charge +13, only 10 electrons). Therefore, the pair should be $\mathrm{Mg}$ and $\mathrm{Al}^{3+}$, not Al and $\mathrm{Mg}^{2+}$.Statement B is correct: IUPAC systematic name for element 107 is unnilseptium (107 = unn‑il‑septium).Statement C is correct: Lithium and magnesium show diagonal similarity due to similar ionic sizes and polarising power.Statement D is correct: In $[\mathrm{AlCl}(\mathrm{H_2O})_5]^{2+}$, Al is in +3 oxidation state (since each Cl⁻ is –1, each $\mathrm{H_2O}$ is neutral, overall +2 charge), and it coordinates to 6 ligands (1 Cl⁻ + 5 H₂O), so covalency = 6.Shortcut:For size comparison, remember: For isoelectronic species, higher atomic number → smaller radius. Here $\mathrm{Al}^{3+}$ (Z=13) is smaller than $\mathrm{Mg}^{2+}$ (Z=12) among the cations. Among neutral atoms, $\mathrm{Mg}$ is larger than $\mathrm{Al}$ because atomic radius decreases across a period.Answer:Option A is the incorrect statement.