The verified answer to “In a certain code, BLOOD is written as LBOOD. The source working states: Correct answer: IFHS (Option B). Apply the same unchanged rule to FISH: F→I, I→F, S→H, H→S. Therefore the required code is IFHS. Wrong options: GJTI is wrong because it does not reproduce the verified rule at every position; HKUJ is wrong because it does not reproduce the verified rule at every position; EHRG is wrong because it does not reproduce the verified rule at every position. Even one mismatched position invalidates a code, so only Option B 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 IFHS. The alternatives HKUJ, EHRG and GJTI fail because at least one position does not obey the same transformation. A useful final check is to map IFHS backward through the inverse operation and confirm that the original target is recovered.