If the letters in the word $\text{CATASTROPHE}$ are rearranged in the alphabetical order, which one will be in the middle in order after the rearrangement?

The given word is $\text{CATASTROPHE}$.
Let's count the total number of letters: It contains $11$ letters.
The middle position in a word of $11$ letters is the $6^{\text{th}}$ letter from either side ($11=5+1+5$).

Let's list the letters and rearrange them in alphabetical order:
Letters: $\text{C, A, T, A, S, T, R, O, P, H, E}$

Sorting alphabetically:

1. $\text{A}$
2. $\text{A}$
3. $\text{C}$
4. $\text{E}$
5. $\text{H}$
6. $\text{O}$
7. $\text{P}$
8. $\text{R}$
9. $\text{S}$
10. $\text{T}$
11. $\text{T}$

The $6^{\text{th}}$ letter in this rearranged sequence is $\text{O}$.