Choose the odd one out.

Let's analyze the alphabetical positioning of each pair:
* KL: $K$ ($11$) and $L$ ($12$) are consecutive letters in forward alphabetical order.
* QR: $Q$ ($17$) and $R$ ($18$) are consecutive letters in forward alphabetical order.
* AZ: $A$ ($1\text{st}$ from start) and $Z$ ($1\text{st}$ from end) form an opposite letter pair. They are not consecutive.
* FG: $F$ ($6$) and $G$ ($7$) are consecutive letters in forward alphabetical order.

All choices except AZ consist of consecutive letters. Thus, AZ is the odd pair.