The correct answer is "The tallest peaks of the Alps are taller than the tallest of the Rocky Mountains of the American West"
Explanation:
In grammar, capitalization should be used in the first word of text or in the first word after a period and in proper nouns, this includes using capitalization for the names of people, days of the week and months, brands, natural landmarks, organization, planets, and nationalities. In the case of proper nouns composed by more than one word it is important to capitalize all the words of it, for example in the case of natural landmarks such as "Grand Canyon National Park" or "Rocky Mountains" all the words should be capitalized except if they are articles or conjunctions. Additionally to this, words referring to nationalities such as "Chinese" or "American" should be capitalized, as well as geographical zones such as "North Coast" or "American West".
Considering the previous ideas, in the case of the sentence "The tallest peaks of the Alps are taller than the tallest of the Rocky Mountains of the american West", all words have been correctly capitalized except by the word "American" which is a proper noun or nationality and should be capitalized. Thus, the sentence that shows the correct capitalization for the proper adjective which is "American" of this sentence is " "The tallest peaks of the Alps are taller than the tallest of the Rocky Mountains of the American West".
