Correct Answer: productive

Solution : The first option is the correct choice.

"Futile" means having no result or effect and being incapable of producing any useful result. On the other hand, "productive" refers to something that is capable of producing results, being fruitful, or yielding positive outcomes.

The meanings of the other words are:

Hollow: It means empty or without substance. In contrast to "futile," which implies a lack of effectiveness, "hollow" suggests something lacking depth, sincerity, or significance.

Barren: It means unproductive or incapable of producing offspring. As an antonym for "futile," "barren" emphasises a lack of fertility or productivity.

Worthless: It means having no value or worth. When used as an antonym for "futile," it emphasises the absence of any positive or meaningful outcome.

Therefore, "productive" is the antonym that conveys the opposite meaning to "futile".