Three of the following number-pairs are alike in some manner and hence form a group.
Which number-pair does not belong to that group?
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 - Operations on 13 such as adding/subtracting/ multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

Logic: Second number is reverse of first number.

Check Options:
A) 1234 → 4321 (reverse)
B) 4326 → 6234 (reverse)
C) 3679 → 9763 (reverse)
D) 9123 → 3129 ✘ (reverse should be 3219)

Thus, D does not follow the pattern.

Final Answer:
9123 – 3129

Final Correct Option:
(D)