[Listening extract audio not available in printed QP. Skeleton score in Insert.] Notes X, Y and Z do not belong to the underlying chord. (a) X moves by step...

(a) Note X, which moves by step between two chord tones, is a passing note. [1]

A passing note is a non-chord tone that fills in the gap between two chord tones by stepwise motion (moving up or down by a second). It typically falls on a weak beat or a weak part of the beat, creating a smooth, conjunct connection between two notes of the harmony. Passing notes can be diatonic (using notes from the prevailing key) or chromatic (using sharps or flats outside the key). They are one of the most common and fundamental types of non-chord tone in tonal music.

(b) Note Y, which steps away from a chord tone and returns, is an auxiliary note (also accepted: neighbour note). [1]

An auxiliary note (or neighbour note) is a non-chord tone that moves by step away from a chord tone and then returns to the same chord tone. It can be upper (stepping up and back) or lower (stepping down and back). In the score, the quaver pair around Y shows this characteristic "away and back" motion. Auxiliary notes add melodic decoration without moving the melody to a new pitch, unlike passing notes which bridge between two different chord tones.

(c) Note Z, which is tied across the barline and resolves downward, is a suspension. [1]

A suspension occurs in three stages: preparation (the note sounds as part of the first chord), suspension (the note is held over or tied into the next chord, where it becomes a dissonance), and resolution (the held note steps down to a note that belongs to the new chord). The tie across the barline in the score shows the note being sustained from one harmony into the next, and its downward resolution follows the standard pattern. Suspensions create controlled moments of tension and release, and are named by the intervals they form (e.g., a 4-3 suspension, where the suspended note is a 4th above the bass and resolves to a 3rd).