Find the missing term in the following series:
$$\text{ZA, ?, VE, TG}$$

Let's split each term into its constituent first and second letters:
First letter tracking: $\text{Z, ?, V, T}$
Alphabetical positions are: $\text{Z}=26$, $\text{V}=22$, $\text{T}=20$.
The pattern is decreasing by $2$:

$$26-2=24=\text{X}$$

$$24-2=22=\text{V}$$

So, the first letter is $\text{X}$.

Second letter tracking: $\text{A, ?, E, G}$
Alphabetical positions are: $\text{A}=1$, $\text{E}=5$, $\text{G}=7$.
The pattern is increasing by $2$:

$$1+2=3=\text{C}$$

$$3+2=5=\text{E}$$

So, the second letter is $\text{C}$.

Combining both, the missing term is $\text{XC}$.