The correct option is C barren
Fertile means producing or capable of producing abundant vegetation or crops. The opposite of fertile is barren, or too poor to produce much or any vegetation. Hence, Option C is correct. Among the rest of the options, unproductive means not producing or able to produce large amounts of goods, crops, or other commodities, dry means free from moisture or liquid; not wet or moist, deserted means (of a place) empty of people. These options do not express this antonym, hence incorrect