Choose the odd one out.

Let's analyze the relationship between the letters in each option:
* KL: $K$ and $L$ are consecutive letters in alphabetical order ($11$ and $12$).
* QR: $Q$ and $R$ are consecutive letters in alphabetical order ($17$ and $18$).
* AZ: $A$ and $Z$ are opposite pairs (first from the start and first from the end). They are not consecutive.
* FG: $F$ and $G$ are consecutive letters in alphabetical order ($6$ and $7$).

Since AZ consists of opposite letters while all other pairs consist of consecutive alphabetical letters, AZ is the odd one out.