The sketches I to IV in figure below show sound waves, all formed in the same time interval.

Which diagram shows

(i) a note from a musical instrument,

(ii) a soft (or feeble) note,

(iii) a bass (or low frequency) note.

(i) Note from a musical instrument is shown by figure IV as the sketch has subsidiary notes and all musical instruments produce subsidiary notes.

(ii) Soft (or feeble) note is shown by figure I, as we can observe from the wave form that it has the lowest amplitude.

(iii) Bass (or low frequency) note is shown by Figure II, as we can observe from the wave form that it has the lowest frequency.