Final answer:
The Internal Revenue Code section has the highest tax validity, serving as the legal authority on federal tax law, with Regulations, Revenue Procedures, and Revenue Rulings following in that order of authority.
Step-by-step explanation:
Among the listed sources of tax law, the Internal Revenue Code section holds the highest tax validity. The Internal Revenue Code (IRC) is a federal statute that provides legal authority on federal tax matters and is arranged by topic. Regulations, which are issued by the Treasury Department, interpret and give more detail to the Internal Revenue Code. These regulations can provide significant guidance and carry substantial weight, but they must be consistent with the IRC. Revenue Procedures are statements of procedure that affect the rights or duties of taxpayers or other members of the public under the law and can be very important in specific scenarios. Revenue Rulings, on the other hand, are the IRS's official interpretations of how the law applies in particular situations; while they are authoritative, they are not as strong as the IRC itself or Regulations.