Step 1: Understanding the S\(_{N}\)2 mechanism.
The S\(_{N}\)2 (bimolecular nucleophilic substitution) mechanism involves a nucleophile attacking the electrophilic carbon from the side opposite the leaving group, leading to a complete inversion of the molecule's configuration. This backside attack forces a flip in the stereochemistry.
Step 2: Evaluation of each option.
- Option 1: Retention of configuration: This is characteristic of the S\(_{N}\)1 mechanism, where the carbocation intermediate allows for nucleophilic attack from either face. S\(_{N}\)2 reactions do not result in retention.
- Option 2: Racemic mixture: A racemic mixture usually arises from the S\(_{N}\)1 mechanism due to the planar carbocation intermediate, which can be attacked from either side. S\(_{N}\)2 reactions, conversely, yield only inversion.
- Option 3: Inversion of configuration: This option accurately describes the S\(_{N}\)2 mechanism. The nucleophile's attack from the rear of the leaving group causes the observed inversion.
- Option 4: Formation of carbocation: Carbocation formation is central to the S\(_{N}\)1 mechanism. The S\(_{N}\)2 mechanism proceeds without the formation of any carbocation intermediate.
Step 3: Conclusion.
When an optically active alkyl halide undergoes S\(_{N}\)2 substitution, the outcome is always inversion of configuration.
Final Answer: \[\boxed{\text{The correct answer is inversion of configuration.}}\]