To find the pattern, compare ROBUST with its coded form QNATRS:
R → Q
O → N
B → A
U → T
S → R
T → S
Each letter shifts backward by 1 position in the alphabet.
To find which word codes to ZXCMP, reverse the process by shifting each letter forward by 1 position:
Z → A (wrapping around from Z to A)
X → Y
C → D
M → N
P → Q
The original word is AYDNQ.
Verification using the coding pattern on AYDNQ:
A → Z (shifting backward by 1, wrapping around)
Y → X
D → C
N → M
Q → P
This gives ZXCMP ✓
Therefore, the answer is Option 2: AYDNQ.
 NTA has marked Option 2 right.