NEET UG 2017 — Chemistry Inorganic Chemistry

2017mcqeasy

The correct increasing order for the wavelengths of absorption in the visible region for the complexes of ${\mathrm{Co}}^{3+}$ is:

Official previous-year question

Held on 30 Apr 2017 · Verified 9 Jul 2026.

Options

A
${[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$
B
${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}$
C
${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}$
D
${[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$

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Solution

The order of the ligand in the spectrochemical series

${H}_{2}O<{\mathrm{NH}}_{3}<\mathrm{en}$

Absorbed wavelength $\text{∝}\frac{1}{\mathrm{Absorbed}\mathrm{energy}}$

Thus, the order of observed energy is:

${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}<{[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}<{[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}$

Hence, the wavelength absorbed will be in the opposite order i.e., ${[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}< {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}< {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$ .

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Options

${[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$

${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}$

${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}, {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}$

${[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}, {[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}, {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$

Solution

The order of the ligand in the spectrochemical series

${H}_{2}O<{\mathrm{NH}}_{3}<\mathrm{en}$

Absorbed wavelength $\text{∝}\frac{1}{\mathrm{Absorbed}\mathrm{energy}}$

Thus, the order of observed energy is:

${[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}<{[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}<{[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}$

Hence, the wavelength absorbed will be in the opposite order i.e., ${[\mathrm{Co}{(\mathrm{en})}_{3}]}^{3+}< {[\mathrm{Co}{({\mathrm{NH}}_{3})}_{6}]}^{3+}< {[\mathrm{Co}{({H}_{2}O)}_{6}]}^{3+}$ .

NEET UG 2017 — Chemistry Inorganic Chemistry

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NEET UG 2017 — Chemistry Inorganic Chemistry

Options

Did you get this right?

Solution

Your note

NEET UG Inorganic Chemistry in other years

More NEET UG Inorganic Chemistry questions

Other Chemistry topics for NEET UG

Physical Chemistry

Organic Chemistry

Keep practicing Inorganic Chemistry