Final answer:
The correct option is 2. The bell of the stethoscope is used to listen to low-pitched extra sounds. The bell of the stethoscope is used to listen to low-pitched extra sounds during cardiac auscultation.
Step-by-step explanation:
The part of the stethoscope used to listen to low-pitched extra sounds is the bell. The bell of the stethoscope is a small, cup-shaped attachment that is placed on the patient's chest. It is designed to pick up low-frequency sounds, such as heart murmurs or abnormal lung sounds.
When using the stethoscope, the clinician places the bell on the patient's chest and listens for any abnormal sounds.