Which of the following sentences is correct?

The correct answer is Option (4) → Please stay inside the classroom until the bell rings for the lunch break.

“Until” without “not”:

• “Until” means “up to the time when”.
• The part after it does not take “not”. We say “until the bell rings”, not “until the bell does not ring”.

Why the Other Options are Incorrect?

Option 1: Both my father as well as my uncle work at the same bank in Lucknow. — Incorrect. “Both” is paired with “and”, not with “as well as”.
Corrected: Both my father and my uncle work at the same bank in Lucknow.

Option 2: The thick fog prevented the flight to land at Amritsar on time. — Incorrect. “Prevent” is followed by “from” + the -ing form of the verb.
Corrected: The thick fog prevented the flight from landing at Amritsar on time.

Option 3: Despite of his fever, Kabir went to school for the unit test. — Incorrect. “Despite” is used without “of”. Only “in spite” takes “of”.
Corrected: Despite his fever, Kabir went to school for the unit test.