Final answer:
The word 'island' is not a proper noun, unlike 'Iceland' and 'Ireland' which are proper nouns referring to specific countries.
Step-by-step explanation:
Among the options provided, "island" is not a proper noun, whereas both "Iceland" and "Ireland" are proper nouns. Proper nouns are specific names for particular people, places, organizations, or sometimes things, and they are always capitalized. "Iceland" and "Ireland" refer to specific countries and are thus capitalized, while "island" is a common noun referring to any landmass surrounded by water and is not capitalized unless it is part of a proper noun, such as in 'Rhode Island'.