What is Rh factor ?

Explanation

### Step-by-Step Solution:

1. **Definition of Rh Factor**: The Rh factor, also known as the Rhesus factor, is a specific protein that can be present on the surface of red blood cells (RBCs) in humans.

2. **Blood Group System**: The Rh factor is part of the broader Rh blood group system, which categorizes blood types based on the presence or absence of specific antigens on the RBCs.

3. **Antigens on RBCs**: Red blood cells can carry different types of antigens, such as A, B, or O. For example, if a red blood cell has the A antigen, it is classified as type A blood.

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