Explanation
The correct spelling is B: Guarantee.
The word "guarantee" means to provide a formal assurance or promise, usually with regard to a product, service, or agreement. It is a commonly used word in English and is spelled with two "u"s, not one.
Option A "Gaurantee" is misspelled with an "a" instead of the second "u". Option C "Garuntee" is also misspelled with an "a" instead of the second "u" and with an "n" instead of an "a". Option D "Guaruntee" is misspelled with an "n" instead of an "a".
Therefore, the correct spelling of the word is B: Guarantee.