The question asks for the word that is spelt incorrectly.
Professional is spelt correctly, meaning relating to a profession.
Combat is spelt correctly, meaning to fight or struggle against something.
Immigrete is spelt incorrectly; the correct spelling is
Immigrate, meaning to come to live permanently in a foreign country.
Relevant is spelt correctly, meaning closely connected or appropriate to the matter at hand.
Therefore, the incorrectly spelt word is
Immigrete, which corresponds to option C.