For a rainy day means for a future time of need. 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: For a rainy day can refer to a situation involving for a future time of need.
• Story example: A writer may use For a rainy day when describing a situation involving for a future time of need.
• Exam example: When a sentence contains For a rainy day, choose the meaning “for a future time of need.”