Find the odd letters cluster from the given options.

Let us inspect the rank difference patterns between the letters of each cluster:
* ECA: $\text{E}(5)\stackrel{-2}{\to }\text{C}(3)\stackrel{-2}{\to }\text{A}(1)$ (Decreasing order with a difference of $-2$)
* QOM: $\text{Q}(17)\stackrel{-2}{\to }\text{O}(15)\stackrel{-2}{\to }\text{M}(13)$ (Decreasing order with a difference of $-2$)
* VTR: $\text{V}(22)\stackrel{-2}{\to }\text{T}(20)\stackrel{-2}{\to }\text{R}(18)$ (Decreasing order with a difference of $-2$)

Now let's check GIK:

* $\text{G}(7)\stackrel{+2}{\to }\text{I}(9)\stackrel{+2}{\to }\text{K}(11)$ (Increasing order with a difference of $+2$)

Since GIK follows an ascending alphabetical step pattern while all others follow a descending pattern, GIK is the odd one out.