Which of the following describes the chord format of a Perfect Authentic Cadence (PAC)?

A Perfect Authentic Cadence (PAC) is characterized by a progression from the dominant chord (V) to the tonic chord (I), with both chords presented in root position. This root position requirement ensures a strong resolution from tension to stability, which is essential for establishing the tonal center of the music. The dominant chord leading to the tonic creates a compelling sense of closure, which is one of the hallmark features of a PAC.

Having both chords in root position means that the bass notes of the chords are the fundamental pitches of those chords (for example, the V chord would feature the note corresponding to its root in the bass, followed directly by the root of the I chord). This clarity and strength of sound further emphasize the authentic nature of the cadence, solidifying it as a definitive end to a musical phrase.

In contrast, other features like inversions, passing tones, or ambiguous chords do not contribute to the defining qualities of a PAC. For example, one chord being in a different inversion would weaken the clarity that a root position provides. Similarly, while passing tones and ambiguity might create interest within a piece, they do not pertain to the strict and conclusive nature required for a Perfect Authentic Cadence.