Correct Answer: ULTRAIST

Solution : Given:
ULTRANATIONALISM

Now, let's compare all the option words with the word ULTRANATIONALISM –
First option: ULTRAMONTANE; All the letters of ULTRAMONTANE are not present in the word ULTRANATIONALISM . E is not present in ULTRANATIONALISM.
Second option: ULTRAMODERN; All the letters of ULTRAMODERN are not present in the word ULTRANATIONALISM. D and E are not present in ULTRANATIONALISM. Two R are present in ULTRAMODERN but only one R is present in ULTRANATIONALISM​​​​​​.
Third option: ULTRAIST; All the letters of ULTRAIST are present in the word ULTRANATIONALISM .
Fourth option: ULULATE; All the letters of ULULATE are not present in the word ULTRANATIONALISM . Two U are present in ULULATE and only one U is present in ULTRANATIONALISM and E is also not present in ULTRANATIONALISM.

So, the word ULTRAIST can be formed using the word ULTRANATIONALISM. Hence, the third option is correct.