Four letter-clusters have been given out of which three are alike in some manner, while one is different. Choose the odd one.

Let's evaluate the structural patterns of the options by writing down alphabetical positions:
* HJLN: $\text{H}(8)\stackrel{+2}{\to }\text{J}(10)\stackrel{+2}{\to }\text{L}(12)\stackrel{+2}{\to }\text{N}(14)$ — Step sizes are constant ($+2,+2,+2$).
* PRTV: $\text{P}(16)\stackrel{+2}{\to }\text{R}(18)\stackrel{+2}{\to }\text{T}(20)\stackrel{+2}{\to }\text{V}(22)$ — Step sizes are constant ($+2,+2,+2$).
* OQRT: $\text{O}(15)\stackrel{+2}{\to }\text{Q}(17)\stackrel{+1}{\to }\text{R}(18)\stackrel{+2}{\to }\text{T}(20)$ — Step sizes vary ($+2,+1,+2$).
* BDFH: $\text{B}(2)\stackrel{+2}{\to }\text{D}(4)\stackrel{+2}{\to }\text{F}(6)\stackrel{+2}{\to }\text{H}(8)$ — Step sizes are constant ($+2,+2,+2$).

Clearly, OQRT breaks the uniform pattern followed by the other three options.