Final answer:
An unknown blood type that reacts only with anti-Rh antiserum would be classified as Rh positive (Rh+).
Step-by-step explanation:
An unknown blood type that reacts only with anti-Rh antiserum would be classified as Rh positive (Rh+).
The Rh blood group is defined by the presence (+) or absence (-) of the Rh antigen on red blood cells. Most people have the Rh antigen and are Rh+.
If the unknown blood type reacts with anti-Rh antiserum only, it indicates the presence of the Rh antigen, leading to the classification of Rh+.