The letter-cluster pair that does NOT belong to the group is JO - LS.
The relationship between the letters in the correct pairs is based on alphabetical position mapping (Opposite Letters / Alphabetical Pairs).
When you pair the alphabet from start to finish (A↔Z,B↔Y,…), each letter has a unique counterpart. The correct pattern takes the opposite of the first letter and shifts it backward or forward to find the second letter.
Let's break down each pair:
HT - RC
QC - AL
CO - MX
JO - LS
While HT-RC, QC-AL, and CO-MX all utilize a system of backward steps from their true alphabetical opposites for their primary character, JO-LS breaks the rule by moving forward in steps instead.