Which of the following refers to a legal obligation to adhere to a standard of care in professional practice?

The phrase "duty of due care" specifically relates to the legal obligation placed upon professionals to meet a standard of care that a reasonable person would provide in similar circumstances. In professional practice, this duty encompasses the responsibility to act in the best interest of clients and ensure that services are rendered safely and competently.

This concept is foundational in areas such as healthcare, law, and various other professional fields, where practitioners are expected to perform their duties to a certain standard to prevent harm to others. Violations of this duty can lead to claims of negligence if a client suffers harm as a result of inadequate care.

The other options, while related to legal and professional standards, do not precisely define this legal obligation. Legal liability involves the responsibility for actions or omissions that result in harm, proximate cause connects actions to their legal consequences, and expectation of care refers to what clients might anticipate in terms of service delivery but does not encapsulate the specific legal obligations inherent in professional practice.