Isomers through Nucleophillic substitution

If a single active optical isomer of 2-chlorobutane were to undergo a nucleophillic substitution reaction with iodide ions, how many optical isomers are present in the product? A mixture? Or just a single isomer?


My attempt:
Iodine can only approach the carbon atom from the opposite side of chlorine(the point at which chlorine is bonded)due to repulsion. So a single isomer is obtained as a product.


However, many of my friends are saying my logic is incorrect. Can somebody please clarify this?


