Which behavior exemplifies neglect of a vulnerable adult?

The behavior that exemplifies neglect of a vulnerable adult is the failure to protect them from others' harm. This indicates a critical lapse in duty of care, as the caregiver or individual responsible for the vulnerable adult's wellbeing has an obligation to ensure their safety and security. Neglect in this context encompasses any action or inaction that results in the individual being exposed to abuse, exploitation, or harm from external sources.

In examining other options, while ignoring complaints of pain, overlooking hygiene issues, and refusing to let them speak could reflect inadequate care or poor treatment, they do not directly represent the failure to safeguard a vulnerable adult from external risks. Neglect particularly pertains to situations where the individual might be exposed to immediate and significant dangers, highlighting the caregiver's responsibility to intervene and protect. This underscores the essential nature of vigilance and proactive behavior in the care of vulnerable adults.