Medium MCQ +4 / -1 PYQ · JEE Mains 2023

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

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

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:

  1. A $\mathrm{A}$ is false but $\mathrm{R}$ is true Correct answer
  2. B Both $\mathrm{A}$ and $\mathrm{R}$ are true but $\mathrm{R}$ is NOT the correct explanation of $A$
  3. C Both $\mathrm{A}$ and $\mathrm{R}$ are true and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
  4. D $\mathrm{A}$ is true but $\mathrm{R}$ is false

Solution

<p>Assertion A : $\left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+}$ absorbs at a lower wavelength of light with respect to $$\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}$$.</p> <p>Given that H<sub>2</sub>O is a stronger field ligand than Cl<sup>-</sup>, 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.</p> <p>Reason R : It is because the wavelength of the light absorbed depends on the oxidation state of the metal ion.</p> <p>While it&#39;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 (H<sub>2</sub>O vs Cl<sup>-</sup>). Therefore, the Reason R is not providing the correct explanation for Assertion A.</p> <p>So, the correct answer would be:</p> <p>Option A : A is false but R is true.</p>

About this question

Subject: Chemistry · Chapter: Coordination Compounds · Topic: Ligands and Coordination Number

This question is part of PrepWiser's free JEE Main question bank. 173 more solved questions on Coordination Compounds are available — start with the harder ones if your accuracy is >70%.

Drill 25 more like these. Every day. Free.

PrepWiser turns these solved questions into a daily practice loop. Chapter-wise drills, full mocks, AI doubt chat. No auto-renew.

Start free →