How should a cocktail be prepared when served on the rocks?

When a cocktail is served "on the rocks," it means that it is poured over ice in a glass. The preferred preparation involves combining the ingredients of the cocktail in a way that allows them to mix properly and chill while also being served with ice. A full 3 oz. recipe in a highball glass is appropriate because highball glasses are designed for cocktails that are served over ice. This presentation allows the drinker to enjoy the beverage at the optimal temperature while the ice helps dilute the drink slightly over time, enhancing flavors without overwhelming them.

The other choices do not align with the typical preparation for cocktails served on the rocks. Shaking a drink and serving it in a martini glass is more suited for cocktails that are strained and served without ice. Mixing with tonic water is specific to certain cocktails but does not define the method of serving them on the rocks. Finally, serving in a chilled coupe glass is usually reserved for cocktails that are served straight up, not over ice. This context helps reinforce the correct understanding of how cocktails should be prepared and served based on the method specified.