The nitrogenous base found in RNA but not DNA is uracil (U).

Here's why:

* DNA uses thymine (T) as one of its four bases, along with adenine (A), guanine (G), and cytosine (C).

* RNA uses uracil (U) instead of thymine, along with adenine (A), guanine (G), and cytosine (C).

Uracil pairs with adenine in RNA just like thymine does in DNA.