Which of the following words cannot be formed using each letter of the given word "REACHABLE" only once?

Let's list the available letter counts in the word REACHABLE:
* R: 1, E: 2, A: 2, C: 1, H: 1, B: 1, L: 1

Now let's check each option:

* CHANGE: Contains the letter N. There is no letter N in REACHABLE. Thus, this word cannot be formed.
* CLEAR: C(1), L(1), E(1), A(1), R(1) $\to$ All are present.
* REACH: R(1), E(1), A(1), C(1), H(1) $\to$ All are present.
* EACH: E(1), A(1), C(1), H(1) $\to$ All are present.

Hence, CHANGE cannot be formed.