One part of the following sentence has an error. Choose that part.

The correct answer is Option (3) → without obtaining none

Without is already negative (it means "not having"). Putting none after it makes a double negative. After a negative word, any is used: "without obtaining any of the necessary documents".

Option 1: Rohan will be suspended because — No error. The future passive "will be suspended" is right.

Option 2: he opened an account — No error.

Option 3: without obtaining none — Error. "none" should be "any".

Option 4: of the necessary documents — No error.

Corrected: Rohan will be suspended because he opened an account without obtaining any of the necessary documents.
Example: She left without saying anything to anyone.