Final answer:
The oculus in the Camera degli Sposi is a painted illusion of a window that is part of Andrea Mantegna's trompe l'oeil ceiling fresco, demonstrating the use of linear perspective in Renaissance art.
Step-by-step explanation:
The true statement about the oculus in the Camera degli Sposi in the Ducal Palace in Mantua, painted by Andrea Mantegna, is that it is a window (option c). This oculus is part of the trompe l'oeil ceiling fresco that Mantegna painted, which creates the illusion of an open sky above the viewer. Unlike the statements related to lenses, battles, or religious symbols, the correct statement specifically relates to the architectural feature that allows light to enter a dome or ceiling. In the context of the Camera degli Sposi, Mantegna's masterful work is a prime example of the Renaissance's exploration of linear perspective and how it can be manipulated to create a convincing illusion of three-dimensional space on a two-dimensional surface.