Die Landeshauptstadt von Rheinland-Pfalz heißt …

Why this is the correct answer

Mainz is the state capital of Rhineland-Palatinate and the seat of its state parliament and government. Although cities like Koblenz and Kaiserslautern may be better known to some, Mainz holds the official capital status. Mainz is also famous as the birthplace of Johannes Gutenberg and the invention of the printing press.