If the letters in the word POWERFUL are rearranged as they appear in the English alphabets, the position of how many letters will remain unchanged after the rearrangement?

Let's list the original positions of the letters in the word POWERFUL:
1. P
2. O
3. W
4. E
5. R
6. F
7. U
8. L

Sorting the letters alphabetically: E, F, L, O, P, R, U, W.

Now let's align the original word and the rearranged word side-by-side to compare:

* P $\to$ E
* O $\to$ F
* W $\to$ L
* E $\to$ O
* R $\to$ P
* F $\to$ R
* U $\to$ U (Unchanged)
* L $\to$ W

Only the letter 'U' remains in its original position ($7\text{th}$ index). Therefore, the position of exactly one letter remains unchanged.