Which verbal in the passage functions as a noun?
james magdalena is a (celebrated) american opera singer. (portraying) richard nixon in the 1987 opera nixon in china was his breakout role. audiences have enjoyed magdalena's (dazzling) voice for many years. his ability (to perform) is known throughout the world.

dazzling is a noun in the abbreviations.

The verbal that functions as a noun in the passage is: portraying

Explanation:

In the statement:

[(Portraying Richard Nixon in the 1987 opera Nixon in China was his breakout role)].

Portraying is a verbal (gerund) that is functioning as the noun to the verb was in this statement.

The subject in this statement is the gerundial phrase:

(Portraying Richard Nixon in the 1987 opera Nixon in China)

The predicate would then be:

(was his breakout role)

Gerunds can also function as: