The verified answer to “In a certain code, BIRD is written as CHSC. How will PLANE be written in that code?” is QKBMF, option D. The source working states: Correct answer: QKBMF (Option A). Apply the same unchanged rule to PLANE: P→Q, L→K, A→B, N→M, E→F. Therefore the required code is QKBMF. Wrong options: QMBOF is wrong because it does not reproduce the verified rule at every position; RNCPG is wrong because it does not reproduce the verified rule at every position; OKZMD is wrong because it does not reproduce the verified rule at every position. Even one mismatched position invalidates a code, so only Option A is correct. This observation must be confirmed across every available letter position or every consecutive term before it is applied to the missing code. Applying the verified rule to the target expression produces QKBMF. The alternatives QMBOF, RNCPG and OKZMD fail because at least one position does not obey the same transformation. A useful final check is to map QKBMF backward through the inverse operation and confirm that the original target is recovered.