In an SN₂ reaction, a nucleophile attacks an electrophilic carbon atom, causing the carbon to become chiral. The nucleophile attacks from the side opposite the leaving group, causing the configuration of the stereocenter to invert. This inversion of configuration results in the product having the opposite stereochemistry compared to the starting material. The SN₂ reaction is a stereospecific reaction, meaning that the stereochemistry of the starting material determines the stereochemistry of the product.

In an SN₂ reaction, a nucleophile attacks an electrophilic carbon atom, causing the carbon to become chiral. The nucleophile attacks from the side opposite the leaving group, causing the configuration of the stereocenter to invert. This inversion of configuration results in the product having the opposite stereochemistry compared to the starting material. The SN2 reaction is stereospecific, meaning that the stereochemistry of the starting material determines the stereochemistry of the product.

Retention configuration refers to a situation in which the product of a reaction has the same stereochemistry as the starting material. In an SN₂ reaction, retention configuration occurs when the nucleophile attacks the electrophilic carbon from the same side as the leaving group. However, this is not a common occurrence in SN₂ reactions.

The product in an SN₂ reaction is not formed with 50% retention in configuration. In an SN₂ reaction, the product will have the opposite stereochemistry as the starting material when there is retention in configuration. However, retention in configuration is not a common occurrence in SN₂ reactions.

The product in an SN₂ reaction is formed with 100% inversion in configuration. In an SN₂ reaction, the nucleophile attacks the electrophilic carbon from the side opposite to the leaving group, resulting in inversion of the configuration at the stereocenter. Therefore, the product will have the opposite stereochemistry as the starting material.