Final answer:
The noun clause in the sentence is b) "Whoever finishes his dinner first" and acts as the subject of the sentence. Noun clauses can function in various roles within a sentence and can begin with words like 'who' or 'whatever.'
Step-by-step explanation:
In the sentence "Whoever finishes his dinner first gets to serve dessert," the noun clause is "Whoever finishes his dinner first". This clause is functioning as the subject of the sentence. It's a noun clause because it contains a subject ("whoever") and a verb ("finishes"), and it takes the place of a noun within the sentence. In English grammar, noun clauses can act as subjects, objects, or complements, and they often start with words like 'who,' 'whom,' 'whoever,' 'whatever,' 'whichever,' 'that,' 'whether,' or 'what.'