Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The total number of geometrical isomers shown by [Co(en)$_2$Cl$_2$]$^+$ complex ion is three.
Reason (R): [Co(en)$_2$Cl$_2$]$^+$ complex ion has an octahedral geometry.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. (A) is correct but (R) is not correct.
• C. (A) is not correct but (R) is correct.
• D. Both (A) and (R) are correct but (R) is not the correct explanation of (A).

Answer 1

The Correct Option is C

The given question involves understanding the geometrical isomers of a coordination complex.

Let's analyze the Assertion (A) and the Reason (R) provided:

1. Assertion (A): The total number of geometrical isomers shown by \([\text{Co(en)}_2\text{Cl}_2]^+\) complex ion is three.
   • \([\text{Co(en)}_2\text{Cl}_2]^+\) is an octahedral complex.
   • The ligand 'en' is ethylenediamine, a bidentate ligand. It can form chelates with the metal ion.
   • In an octahedral complex, \([\text{Co(en)}_2\text{Cl}_2]^+\) can theoretically show cis and trans isomers.
   • However, for \([\text{Co(en)}_2\text{Cl}_2]^+\), only two geometrical isomers are possible: cis and trans.
2. Reason (R): \([\text{Co(en)}_2\text{Cl}_2]^+\) complex ion has an octahedral geometry.
   • This is true. The coordination number is 6, which typically corresponds to an octahedral geometry.

Based on the analysis:

• The Assertion (A) is not correct as the number of geometrical isomers is overstated.
• The Reason (R) is correct as [Co(en)₂Cl₂]⁺ indeed has an octahedral geometry, but it does not justify the incorrect assertion about the number of isomers.

Therefore, the most appropriate answer is:

(A) is not correct but (R) is correct.

Answer 2

The complex ion \([Co(en)_2Cl_2]^+\) has an octahedral geometry. However, it shows only two geometrical isomers:

• Cis-isomer: Both chloride ligands are adjacent to each other.
• Trans-isomer: Chloride ligands are opposite to each other.

This refutes the assertion that it shows three geometrical isomers. Thus, (A) is incorrect. However, the reason (R) stating that the complex has an octahedral geometry is true.

Final Answer: (3) (A) is not correct but (R) is correct.