AIIMS 2006 Chemistry Isomerism Assertion Reason Question

To address the question regarding the assertion and reason related to the coordination compound $[Co(NO_2)_3(NH_3)_3]$, let's break down the concepts involved and clarify why the correct answer is A.

Explanation of the Assertion and Reason

Assertion: $[Co(NO_2)_3(NH_3)_3]$ does not show optical isomerism.

Reason: It has a plane of symmetry.

Understanding Optical Isomerism

Optical isomerism occurs in compounds that are chiral, meaning they cannot be superimposed on their mirror images. For a compound to be chiral, it must lack any plane of symmetry.

Analysis of the Coordination Compound

1. Geometry of $[Co(NO_2)_3(NH_3)_3]$:

   • Cobalt (Co) typically exhibits an octahedral coordination geometry when it forms complexes with six ligands.
   • In this case, we have three nitrito ($NO_2^-$) ligands and three ammine ($NH_3$) ligands.

2. Symmetry Considerations:

   • When you arrange three identical $NO_2^-$ ligands and three identical $NH_3$ ligands in an octahedral field, the resulting complex does demonstrate symmetry.
   • Specifically, it has a plane of symmetry that divides the complex into two mirror-image halves. This plane of symmetry prevents the complex from being chiral.

Since $[Co(NO_2)_3(NH_3)_3]$ possesses a plane of symmetry, it does not exhibit optical isomerism. Thus, the assertion is true, and the reason is also true, providing the correct explanation for the assertion.

Verification of the Correct Answer

Given that both the assertion and the reason are true, and the reason correctly explains why the assertion is true, the answer is:

A) if both assertion and reason are true and reason is the correct explanation of the assertion.

Clarification of Other Options

1. Option B: If both assertion and reason are true but reason is not the correct explanation of the assertion.

   • This is incorrect because the reason does indeed explain the assertion; the presence of a plane of symmetry is the reason for the lack of optical isomerism.

2. Option C: If assertion is true, but reason is false.

   • This is incorrect because both the assertion and reason are true.

3. Option D: Both assertion and reason are false statements.

   • This is incorrect as both statements have been established as true.

Conclusion

In summary, the coordination compound $[Co(NO_2)_3(NH_3)_3]$ does not show optical isomerism due to the presence of a plane of symmetry, making both the assertion and reason true and correctly linked. Therefore, the correct answer is A. Understanding the geometrical arrangement and symmetry in coordination compounds is crucial for predicting their isomeric behavior.