In a certain code CERTAIN is coded as XVIGZRM. How is MUNDANE coded in that…

Key rule: Each letter is replaced by its counterpart from the end of the alphabet (A ↔ Z, B ↔ Y, C ↔ X, ...).

Apply this to the word MUNDANE:

• M → N

• U → F

• N → M

• D → W

• A → Z

• N → M

• E → V

Therefore, MUNDANE → NFMWZMV.