Concept:
Each letter is shifted one step backward in the alphabet.
Step 1: Verify pattern using CERTAIN → BFQUZJM.
\[
C \rightarrow B,\ E \rightarrow F,\ R \rightarrow Q,\ T \rightarrow U,\ A \rightarrow Z,\ I \rightarrow J,\ N \rightarrow M
\]
Pattern: Alternate +1 and -1 shifts.
Step 2: Apply same pattern to MUNDANE.
\[
M \rightarrow L\ (-1)
\]
\[
U \rightarrow V\ (+1)
\]
\[
N \rightarrow M\ (-1)
\]
\[
D \rightarrow E\ (+1)
\]
\[
A \rightarrow Z\ (-1)
\]
\[
N \rightarrow O\ (+1)
\]
\[
E \rightarrow D\ (-1)
\]
Step 3: Form coded word.
\[
LVMEZOD
\]
Hence, the coded form is LVMEZOD.