Correct Answer: STOP

Solution : Given:
INSTRUCTOR

Now, let's compare all the option words with the word INSTRUCTOR –
First option: RUST; All the letters of RUST are present in the word INSTRUCTOR.
Second option: TORT; All the letters of TORT are present in the word INSTRUCTOR.
Third option: STOP; P is not present in the word INSTRUCTOR. Therefore, all the letters of STOP are not present in the word INSTRUCTOR.
Fourth option: STINT; All the letters of STINT are present in the word INSTRUCTOR.

So, STOP cannot be formed with the help of the letters of the word INSTRUCTOR. Hence, the third option is correct.