Answer the question according to the letter series given below:
$$\text{H D Y S M W N B Q O C R T B L Z V E G U F}$$

Which two neighbours in the given arrangement are farthest in the alphabetical order?

To find which two adjacent elements (neighbours) are farthest in the standard alphabetical order, let's find the absolute difference between their numerical positional values in the English alphabet:
* Option A (B and Q): Position of $\text{B}=2$, Position of $\text{Q}=17$.

$$\text{Difference}=|2-17|=15$$

* Option B (D and Y): Position of $\text{D}=4$, Position of $\text{Y}=25$.

$$\text{Difference}=|4-25|=21$$

* Option C (U and F): Position of $\text{U}=21$, Position of $\text{F}=6$.

$$\text{Difference}=|21-6|=15$$

* Option D (V and E): Position of $\text{V}=22$, Position of $\text{E}=5$.

$$\text{Difference}=|22-5|=17$$

Comparing the absolute differences, the pair D and Y has the highest separation value ($21$) in the alphabet.