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 question pertains to the geometrical isomerism of a coordination complex.

Analysis of the Assertion (A) and Reason (R):

1. Assertion (A): The total number of geometrical isomers for the complex ion \([\text{Co(en)}_2\text{Cl}_2]^+\) is stated as three.
   • \([\text{Co(en)}_2\text{Cl}_2]^+\) exhibits octahedral geometry.
   • The ligand 'en' (ethylenediamine) is a bidentate ligand capable of chelation.
   • In an octahedral complex, \([\text{Co(en)}_2\text{Cl}_2]^+\) could theoretically exist as cis and trans isomers.
   • However, for \([\text{Co(en)}_2\text{Cl}_2]^+\), only two distinct geometrical isomers, namely cis and trans, are possible.
2. Reason (R): The complex ion \([\text{Co(en)}_2\text{Cl}_2]^+\) possesses octahedral geometry.
   • This statement is accurate. A coordination number of 6 characteristically indicates octahedral geometry.

Conclusion based on the analysis:

• The Assertion (A) is inaccurate due to an overestimation of the number of geometrical isomers.
• The Reason (R) is correct; \([\text{Co(en)}_2\text{Cl}_2]^+\) does have octahedral geometry, but this fact does not validate the incorrect assertion regarding isomer count.

The most fitting response is:

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