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

Let's analyze the letters available in the word “REACHABLE”:
$$\text{A}\to 2,\text{B}\to 1,\text{C}\to 1,\text{E}\to 2,\text{H}\to 1,\text{L}\to 1,\text{R}\to 1$$

Let's check each option:

* CHANGE: Contains the letter 'N', which is not present in the word “REACHABLE”.
* REACH: All letters ($\text{R, E, A, C, H}$) are present.
* CLEAR: All letters ($\text{C, L, E, A, R}$) are present.
* EACH: All letters ($\text{E, A, C, H}$) are present.

Therefore, the word “CHANGE” cannot be formed.