Which section of the following sentence has an error, if any ?
A "swarm of locust (P)has seriously(Q) damaged our crops.(R) No error.(S)

The correct answer is '1' i.e. p .

Key Points   

• The given sentence is: "A "swarm of locust (P)has seriously(Q) damaged our crops.(R) No error.(S)"       
• Let's examine each part to identify any errors:       
• (P) A "swarm of locust: This section contains an error. The collective noun "swarm" indicates a group. When referring to a group of insects like locusts, the noun following "of" should be in its plural form. Therefore, it should be "locusts," not "locust."       
• (Q) has seriously: This part is grammatically correct. "Has" agrees with the singular collective noun "swarm," and "seriously" is an adverb correctly modifying the verb "damaged."      
• (R) damaged our crops.: This part is grammatically correct. "Damaged" is the past participle used correctly, and "our crops" is the direct object.       
• Since an error is found in part (P), option (S) "No error" is incorrect.

Correct sentence: A swarm of **locusts** has seriously damaged our crops.

Additional Information       

• Collective Nouns: Collective nouns (like 'swarm', 'flock', 'herd', 'team', 'committee') refer to a group of individuals. When these nouns are followed by "of" and then another noun, the second noun is typically in its plural form to denote multiple members of the group. For example, "a flock of birds," "a herd of cows," "a team of players."       
• The singular form "locust" refers to one insect, whereas "locusts" refers to multiple. A "swarm" inherently implies multiple insects.