Correct option (a)
Explanation:
PhS- is a strong nucleophile and dimethylformamide (DMf) is a highly polar aprotic solvent. Condition indicates that nucleophilic substitution (SN2) takes place at 2° benzylic place, stereochemically it involves inversion of confi guration.
Aryl group exhibit neighbouring group or can show anchimeric assistance but not possible here due to deactivity imparted by -NO2 and -F . It can be if -OCH3 would have been instead of -NO2
