Find the fourth term of the given alphabet series:
ZXYW, VTUS, RPQO, ________, JHIG

Let us trace the alphabetical position pattern for the first letter of each group:
* $\text{Z }(26)\stackrel{-4}{\to }\text{V }(22)$
* $\text{V }(22)\stackrel{-4}{\to }\text{R }(18)$
* $\text{R }(18)\stackrel{-4}{\to }\text{N }(14)$
* $\text{N }(14)\stackrel{-4}{\to }\text{J }(10)$

The first letter of the missing group is $\text{N}$.

Let us look closely at the configuration within each four-letter group:

* $\text{ZXYW}$: $\text{Z}(26),\text{X}(24),\text{Y}(25),\text{W}(23)$. The pattern is: First letter, then (First $-2$), then (First $-1$), then (First $-3$).
* Let's check with $\text{N}$:
* 1st letter = $\text{N }(14)$
* 2nd letter = $14-2=12⟹\text{L}$
* 3rd letter = $14-1=13⟹\text{M}$
* 4th letter = $14-3=11⟹\text{K}$

Thus, the group becomes $\text{NLMK}$. This completely matches the subsequent group $\text{JHIG}$ since $\text{N}(14)\stackrel{-4}{\to }\text{J}(10)$, $\text{L}(12)\stackrel{-4}{\to }\text{H}(8)$, $\text{M}(13)\stackrel{-4}{\to }\text{I}(9)$, and $\text{K}(11)\stackrel{-4}{\to }\text{G}(7)$.