Go off the rails means start behaving badly or losing control. This answer is correct because the expression has a fixed figurative meaning in English. In an SSC idiom question, students should match the whole phrase with its accepted meaning rather than translate each word separately.

• Classroom example: Go off the rails can refer to a situation involving start behaving badly or losing control.
• Story example: A writer may use Go off the rails when describing a situation involving start behaving badly or losing control.
• Exam example: When a sentence contains Go off the rails, choose the meaning “start behaving badly or losing control.”