This is a nucleophilic substitution reaction where the cyanide ion (CN⁻) attacks the carbon adjacent to the bromine. The reaction proceeds via an SN2 mechanism, leading to inversion of configuration at the chiral center. The bromine is replaced by the cyanide group.

The major product is the inverted stereoisomer: ${\mathrm{NC}}_{}-\mathrm{CH}(\mathrm{CH}{)}_3-\mathrm{CH}{)}_2\mathrm{CH}{)}_3$

Final Answer: The second option.