Step-by-step explanation:
In an authentic cadence, a chord that incorporates the dominant triad (based on the fifth tone of the scale) is followed by the tonic triad (based on the first tone of the scale), V–I; the tonic harmony comes at the end of the phrase.
In the strongest type of authentic cadence, called the perfect cadence, the upper voice proceeds stepwise either upward from the leading tone (seventh degree of the scale) or downward from the second degree to the tonic note, while the lowest voice skips from the dominant note upward a fourth or downward a fifth to the tonic note.
Other arrangements of this harmonic formula—for instance, with the leading tone in an inner part (e.g., the alto or tenor voice in four-part harmony)—are considered less perfect because they are perceived by the listener as less final.