Answer : 1. "Uracil"
Explanation :

Answer: A) Uracil Explanation: A nitrogenous base, or nitrogen-containing base, is an organic molecule with a nitrogen atom that has the chemical properties of a base. The main biological function of a nitrogenous base is to bond nucleic acids together. A nitrogenous base owes its basic properties to the lone pair of electrons of a nitrogen atom.   In DNA, four bases have been found. They are 1. Adenine (A), 2. Guanine (G), 3. Cytosine (C) and 4. Thymine (T).   The first three of these bases are found in RNA also but the fourth which is Uracil (U) is absent in it. RNA contains cytosine and uracil as pyrimidine bases while DNA has cytosine and thymine.