According to MRPC Rule 4.1(b), what is a lawyer prohibited from doing?

The correct answer is that a lawyer is prohibited from assisting a client in committing a fraud or crime as outlined in MRPC Rule 4.1(b). This rule emphasizes a lawyer's duty to maintain honesty and integrity in their practice. Specifically, it prohibits lawyers from offering assistance to their clients that would facilitate or encourage illegal or dishonest conduct.

The rationale behind this rule is clear: lawyers have an ethical responsibility to uphold the law and promote justice. By assisting in fraudulent or criminal behavior, a lawyer undermines the legal system and breaches their professional obligations. This aligns with the fundamental principles of justice and fairness that the legal profession upholds.

The other options do not reflect the prohibitions outlined in Rule 4.1(b). Advising clients on legal matters (first choice) is a core function of a lawyer's role, while testifying as a witness (third choice) is permissible under certain circumstances, contingent on conflicts of interest. Representing a client in legal matters (fourth choice) is also a primary duty of lawyers, provided they do so ethically and within the bounds of the law.