Which varietal is known for its high acidity and is often used in sparkling wines?

Chardonnay is known for its high acidity and is a popular choice for sparkling wines, particularly in the production of Champagne and other traditional method sparkling wines around the world. This varietal's balanced acidity contributes to the freshness and vibrant character of sparkling wine, which is crucial for crispness and longevity.

Chardonnay can also display a wide range of flavors, from green apple and pear in cooler climates to more tropical fruit notes in warmer regions. Its ability to express terroir also makes it a versatile grape, able to be crafted into both still and sparkling styles. The high acidity in Chardonnay is essential in the sparkling wine production process, as it helps to balance the richness that comes from secondary fermentation and aging on the lees.

Other varietals listed, such as Merlot and Cabernet Sauvignon, are generally appreciated for their bold flavors and fruitiness, rather than for their acidity. Sauvignon Blanc does have noticeable acidity, but it is not commonly used in sparkling wine production compared to Chardonnay. This distinction highlights the specific role Chardonnay plays in sparkling wine, making it the correct choice for this question.