Final answer:
The highest ranking legal adviser of the IRS is the Chief Counsel, who is responsible for providing legal guidance on tax matters and overseeing IRS litigation.
Step-by-step explanation:
The correct answer to the question is d. Chief Counsel. The Chief Counsel is the highest ranking legal adviser in the Internal Revenue Service (IRS). This individual provides legal guidance and interpretation of tax law for the IRS and also oversees litigation involving the IRS.
This role is distinct from the Solicitor General, who represents the federal government before the Supreme Court and decides which cases to appeal from lower courts. The Chief Counsel, unlike the Solicitor General, is specifically focused on tax law and IRS matters.