Which wine region in the southern Rhone produces exclusively rosé wines?

Tavel is recognized as the only wine region in the southern Rhône that specializes exclusively in the production of rosé wines. The appellation is known for its distinctive style of rosé, which is often made primarily from Grenache and has a reputation for being full-bodied and capable of aging, unlike many other rosés that are typically lighter and meant for early consumption.

In contrast, the other regions listed produce a variety of styles, including red and sometimes white wines. Lirac, for example, produces red, white, and rosé wines, while Vacqueyras predominantly focuses on red wines but can also produce some white and rosé. Gigondas is primarily known for its robust red wines, though whites and rosés are also part of its offerings. Thus, Tavel stands out for its exclusive focus on rosé, making it the correct answer.