Correct Answer: TRUST

Solution : Given:
ILLUSTRIOUS

Now, let's compare all the option words with the word ILLUSTRIOUS –
First option: LUST; All the letters of the word LUST are present in the word ILLUSTRIOUS.
Second option: TRUST; All the letters of the word TRUST are not present in the word ILLUSTRIOUS. The word ILLUSTRIOUS has only one T but the word TRUST has two T .
Third option: RIOT; All the letters of the word RIOT are present in the word ILLUSTRIOUS.
Fourth option: RUST; All the letters of the word RUST are present in the word ILLUSTRIOUS.

Therefore, TRUST cannot be formed from the word ILLUSTRIOUS. Hence, the second option is correct.