What additional ingredient is used in a Whiskey Sour besides whiskey and sour mix?

In a Whiskey Sour, while whiskey and sour mix (which typically contains lemon juice and simple syrup) are the primary components, an essential addition that enhances the cocktail's flavor and presentation is a cherry. Typically, a maraschino cherry is garnished on the drink, adding a touch of sweetness and visual appeal that complements the tartness of the lemon juice in the sour mix.

The other options, while they may have their own uses in different cocktails, do not serve the same purpose in a Whiskey Sour. Soda water is generally not included as an ingredient in this cocktail, and while ice is a critical component for chilling the drink, it does not add flavor. Lemon juice is already part of the sour mix, so it doesn't count as an additional ingredient. The cherry stands out as a garnish that elevates the Whiskey Sour's overall experience.