There are three primary differences between RNA and DNA:

1. Sugar: RNA contains D-Ribose ($-OH$ at $C_2$), while DNA contains 2-Deoxy-D-ribose ($-H$ at $C_2$).
2. Bases: Both have Adenine, Guanine, and Cytosine. However, RNA has Uracil (U) whereas DNA has Thymine (T).
3. Structure: RNA is generally single-stranded, whereas DNA exists as a double helix.