Correct Answer: CURTAIN

Solution : Given:
UNIVERSALISATION

Now, let's compare all the option words with the word UNIVERSALISATION –
First option: NATION; All the letters of NATION are present in the word UNIVERSALISATION.
Second option: CURTAIN; All the letters of CURTAIN are not present in the word UNIVERSALISATION. C and two T are not present in the word UNIVERSALISATION.
Third option: LIVER; All the letters of LIVER are present in the word UNIVERSALISATION.
Fourth option: AVIATION; All the letters of AVIATION are present in the word UNIVERSALISATION.

So, from the above, only CURTAIN cannot be formed using the letters of the word UNIVERSALISATION. Hence, the second option is correct.