Correct Answer: PEACE

Solution : Given:
IMPRACTICABLE

Now, let's compare all the option words with the word IMPRACTICABLE –
First option: CAPABLE; All the letters of CAPABLE are present in the word IMPRACTICABLE.
Second option: PARTICLE; All the letters of PARTICLE are present in the word IMPRACTICABLE.
Third option: PRACTICAL; All the letters of PRACTICAL are present in the word IMPRACTICABLE.
Fourth option: PEACE; All the letters of PEACE are not present in the word IMPRACTICABLE. Two E are not present in the word IMPRACTICABLE.

So, from the above, only PEACE cannot be formed using the letters of the word IMPRACTICABLE. Hence, the fourth option is correct.