Answer:
Noun clause: whoever is tallest
Function: subject
Step-by-step explanation:
A noun clause is a dependent clause (a group of words containing a subject and a verb and that does not express a complete thought) acting as a noun in a sentence, and usually beginning with the words who, whoever, whom, whomever, how, that, what, whatever, when, where, whether, which, whichever, or why.
“Whoever is tallest” is a noun clause because it has a subject and a verb, it does not express a complete thought, acts as a noun and begins with the word “whoever.” Besides, it is the subject of the sentence because it is the “thing” being dealt with.