Which of the following is a style of mixto tequila?

The correct answer is Gold, as this refers specifically to a style of mixto tequila. Mixto tequila is produced using a blend of at least 51% blue agave and other sugars. Gold tequila, often labeled as "gold" or "joven," is typically a mixto, meaning it has a combination of agave and other sugars, giving it a distinct flavor profile that is usually sweeter and less complex compared to 100% agave tequilas.

In contrast, Blanco tequila is made entirely from blue agave and is unaged, without the inclusion of other sugar sources, and aligns with premium categories rather than mixto. Extra Anejo tequila must be aged for a minimum of three years and is formed from 100% agave, again differing from the mixto definition. The Negroni is a cocktail that comprises gin, vermouth, and Campari, which does not relate to tequila styles at all. Thus, Gold is the only option that fits the criteria for a style of mixto tequila.