In a vacuum means without considering surrounding facts or context. 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: In a vacuum can refer to a situation involving without considering surrounding facts or context.
• Story example: A writer may use In a vacuum when describing a situation involving without considering surrounding facts or context.
• Exam example: When a sentence contains In a vacuum, choose the meaning “without considering surrounding facts or context.”