Correct Answer: To buy something that is worthless.

Solution : The correct choice is the fourth option .

The idiom buy a lemon typically means purchasing an item, usually a product like a car, that turns out to be defective, unsatisfactory, or of poor quality despite appearing good at the time of purchase. This is similar to the meaning given in the fourth option.

Therefore, the most appropriate meaning of the given idiomatic expression is to buy something that is worthless.