Topic: Subject Verb Agreement,

Best Answer Explained in Below-:

The phrase "One-third of the mangoes — rotten." requires a verb that agrees both grammatically and logically with its subject. In this case, the subject is "one-third of the mangoes," which acts as a collective noun phrase.

When we analyze the subject, "one-third" is a singular fraction, but it refers to a plural noun, "mangoes." Therefore, the verb must align with the actual count of the noun, which is plural. The correct choice, "are," is grammatically appropriate because it indicates that the number of mangoes being discussed is more than one.

The phrase could be rephrased as "One-third of the mangoes are rotten," which maintains proper syntax and conveys a clear meaning. If we used "is," it would imply that "one-third" is a singular quantity treated as a whole, which could create confusion. Similarly, "was" and "gets" don't fit the present tense context of the observation about the mangoes. Thus, "are" is the only option that accurately reflects the number and state of the subject, making it the correct answer.