MHTCET 5 May 2025 Shift 2 Paper

Concept:EAN rule states that a complex obeys EAN rule if its effective atomic number equals the atomic number of the nearest noble gas: $18(\mathrm{Ar})$, $36(\mathrm{Kr})$, $54(\mathrm{Xe})$, or $86(\mathrm{Rn})$.The formula used is: $\text{EAN} = Z - \text{oxidation state} + \text{electrons donated by ligands}$.Explanation:For option A: $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$$Z = 27$, oxidation state of Co is $+3$, ligands donate $6 \times 2 = 12$ electrons.EAN $= 27 - 3 + 12 = 36$ (equal to Kr). Obeys EAN rule.For option B: $\mathrm{Cr}(\mathrm{CO})_{6}$$Z = 24$, oxidation state of Cr is $0$, ligands donate $6 \times 2 = 12$ electrons.EAN $= 24 - 0 + 12 = 36$ (equal to Kr). Obeys EAN rule.For option C: $\left[\mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$$Z = 30$, oxidation state of Zn is $+2$, ligands donate $4 \times 2 = 8$ electrons.EAN $= 30 - 2 + 8 = 36$ (equal to Kr). Obeys EAN rule.For option D: $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$$Z = 29$, oxidation state of Cu is $+2$, ligands donate $4 \times 2 = 8$ electrons.EAN $= 29 - 2 + 8 = 35$ (not equal to 36). Does not obey EAN rule.Answer:Option D: $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$ does NOT obey the EAN rule.