Final answer:
The return on investment for an unexercised stock option is -100%, which reflects the total loss of the premium paid for the option by the investor.
Step-by-step explanation:
If a stock option is never exercised, the return on investment generated is -100%. This is based on the idea that an option gives the holder the right, but not the obligation, to buy or sell a certain amount of stock at a predetermined price within a certain timeframe. If the option is not exercised, the investor will lose the entire premium paid for the option. Therefore, the investment is completely lost, resulting in a return of -100%.