In a flash means very quickly. 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 flash can refer to a situation involving very quickly.
• Story example: A writer may use In a flash when describing a situation involving very quickly.
• Exam example: When a sentence contains In a flash, choose the meaning “very quickly.”