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