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AIIMS2019Chemistry-Coordination Compounds

AIIMS 2019 Chemistry Crystal Field Theory MCQ Question

Type: MCQ-conceptual-Medium-Class 12

C+O2(g)→CO2……(i);ΔH=−393 kJmol−1\text{C} + \text{O}_2(\text{g}) \rightarrow \text{CO}_2 \dots\dots(\text{i}); \quad \Delta\text{H} = -393 \text{ kJmol}^{-1}

H2+12O2→H2O,……(ii);ΔH=−287.3 kJmol−1\text{H}_2 + \frac{1}{2}\text{O}_2 \rightarrow \text{H}_2\text{O}, \dots\dots(\text{ii}); \quad \Delta\text{H} = -287.3 \text{ kJmol}^{-1}

2CO2+3H2O→C2H5OH+3O2……(iii);ΔH=1366.8 kJmol−12\text{CO}_2 + 3\text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \dots\dots(\text{iii}); \quad \Delta\text{H} = 1366.8 \text{ kJmol}^{-1}

Find the standard enthalpy of formation of C2H5OH(l)\text{C}_2\text{H}_5\text{OH}(\text{l})

A

281.1 kJ mol−1281.1 \text{ kJ mol}^{-1}

B

−281.1 kJ mol−1-281.1 \text{ kJ mol}^{-1}

C

562.2 kJ mol−1562.2 \text{ kJ mol}^{-1}

D

−562.2 kJ mol−1-562.2 \text{ kJ mol}^{-1}

Correct Answer

Option B

Detailed Explanation

Option B, [Co(NH₃)₆]³⁺, is correct because NH₃ is a stronger field ligand than H₂O and Cl⁻, leading to a larger splitting energy (Δ₀) and thus a shorter wavelength of light absorbed. The order of ligand strength indicates that [Co(CN)₆]³⁻, with the strongest ligand CN⁻, would absorb light at the lowest wavelength, while [Co(NH₃)₅(H₂O)]³⁺ and [Co(NH₃)₅Cl]²⁺, containing weaker ligands, would absorb light at longer wavelengths. Therefore, as the strength of the ligands decreases, the wavelength of absorption increases, making [Co(NH₃)₆]³⁺ the option with the shortest wavelength among the choices provided.

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