MANGO: OCPOQ:: APPLE

The code shifts each letter forward by two places in the alphabet. Check MANGO: M(13) to O(15), A(1) to C(3), N(14) to P(16), G(7) to I(9), O(15) to Q(17). That gives OCPOQ, so the rule is confirmed.

Apply the same +2 shift to APPLE: A to C, P to R, P to R, L to N, E to G. The result is CRRNG, which is option A.

• B (BOOMF): The shifts are inconsistent. A to B is +1, but P to O is -1, and L to M is +1. A single fixed shift cannot produce this.
• C (XYYZW): A to X is a jump of -3 in the wrong direction for a consistent code, and the letters do not follow the +2 pattern.
• D (none of the above): Wrong, because option A fits the rule exactly.

The concept is a letter-shift or substitution code, a standard reasoning and logical-sequence item in the CSAT and reasoning sections. It builds the pattern-recognition habit that also helps in analytical questions in Mains General Studies paper IV.

Trap: Aspirants often test the rule on only one letter pair, or they shift in the wrong direction. Always verify the full word before committing to an answer.