What is the primary characteristic of the souls in Ptolomea?

The primary characteristic of the souls in Ptolomea is that they treacherously betrayed their guests. This region of the ninth circle of Hell, known as the traitors' circle, is specifically designated for those who have committed acts of treachery, especially against people who were close to them, such as friends or family. This betrayal is treated as one of the gravest sins in Dante's moral framework, reflecting a deep violation of trust and loyalty. The punishment here matches the sin, illustrating the theme of poetic justice prevalent throughout Dante's work, where the nature of the sin informs the severity and type of punishment.

In contrast, the other options describe different circles or types of punishments in Dante's Inferno: souls submerged in ice are found in Caina, where those who betrayed family are punished; lustful souls are punished in the second circle; and those eternally tortured by fire are typically found in the circles for the violent and heretical. Each of these options applies to different sins and punishments within Dante's structured vision of Hell, but Ptolomea is clearly defined by treachery against guests, making option B the correct choice.