Final answer:
The highest frequency Rh antigen is the D antigen.
Step-by-step explanation:
The highest frequency Rh antigen is the D antigen. The Rh blood group system has five main antigens - D, C, c, E, and e. Among these, the D antigen is the most significant and commonly found. Individuals who have the D antigen are called Rh-positive (Rh+), while those who lack it are called Rh-negative (Rh-).