The following sentence has been divided into parts. One of them may contain a grammatical error.
They ordered the whole area / to be disinfected / on the earliest.

Correct option is C

Option (c) contains the error.
Explanation:
· The phrase “on the earliest” is incorrect.
· The correct prepositional phrase is “at the earliest,” which means “as soon as possible.”
· → They ordered the whole area to be disinfected at the earliest.
Grammatical Rule Used:
We use “at the earliest” to refer to the earliest possible time.
“On” is used with specific days/dates, not expressions like “the earliest.”
Grammar Booster:
· At the earliest = as soon as possible ✅
· On Monday, on 5th June = correct use of “on” for dates
Example: Please submit the documents at the earliest.