Verified Solution • 2025–26 Session moderate

QJEEM23Ch065d: JEE Main 2023 Chemistry - Class 12 JEEM23Ch065d Solution: Given below are two statements, one is labelled as Assertion A…

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A : [CoCl(NH3)5]2+\left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+} absorbs at lower wavelength of light with respect to [Co(NH3)5(H2O)]3+\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}

Reason R : It is because the wavelength of the light absorbed depends on the oxidation state of the metal ion.

In the light of the above statements, choose the correct answer from the options given below:

Multiple Choice Options

  • A A\mathrm{A} is false but R\mathrm{R} is true
  • B Both A\mathrm{A} and R\mathrm{R} are true but R\mathrm{R} is NOT the correct explanation of AA
  • C Both A\mathrm{A} and R\mathrm{R} are true and R\mathrm{R} is the correct explanation of A\mathrm{A}
  • D A\mathrm{A} is true but R\mathrm{R} is false

Step-by-Step Verified Solution

Assertion A : [CoCl(NH3)5]2+\left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+} absorbs at a lower wavelength of light with respect to [Co(NH3)5(H2O)]3+\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+} .

Given that H2O is a stronger field ligand than Cl-, it would result in a larger splitting of the d-orbitals and hence a larger energy difference. This would lead to absorption at a lower wavelength. Therefore, the Assertion A is false.

Reason R : It is because the wavelength of the light absorbed depends on the oxidation state of the metal ion.

While it's true that the oxidation state can influence the absorption wavelength by affecting the energy levels of the d-orbitals, the difference in the absorption wavelength in this specific case is not primarily due to the oxidation state (the oxidation state of Co in both complexes is the same (+3)), but rather due to the difference in ligand field strength (H2O vs Cl-). Therefore, the Reason R is not providing the correct explanation for Assertion A.

So, the correct answer would be:

Option A : A is false but R is true.

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