Identify the part of the sentence which contains an error. According to the…

Concept: Certain determiners — each, every, either, neither — are distributive determiners. Even though they refer to the members of a group taken one at a time, English grammar requires them to be followed by a SINGULAR countable noun (and a singular verb), never a plural noun.

Application: In the given sentence, the segment ‘every senior citizens’ pairs the distributive determiner ‘every’ with the plural noun ‘citizens’. This determiner–noun mismatch is the grammatical error; the correct form is ‘every senior citizen’ (singular).

• ‘every senior citizens’ — contains the error: the singular distributive determiner ‘every’ cannot take the plural noun ‘citizens’.

• ‘will benefit a lot’ — no error: modal ‘will’ + base verb ‘benefit’ + the adverbial ‘a lot’ is correctly formed.

• ‘from the new scheme’ — no error: preposition ‘from’ + determiner ‘the’ + adjective ‘new’ + noun ‘scheme’ is in standard order.

• ‘According to the finance ministry,’ — no error: a standard introductory prepositional phrase, correctly set off by a comma.

Cross-check: Replacing the plural noun with the singular restores full agreement: ‘According to the finance ministry, every senior citizen will benefit a lot from the new scheme.’ No other change is needed, confirming the error is isolated to this one determiner–noun pairing.