Nucleic Acids

The correct answer is option (A): Uracil
The bases present in DNA are adenine, Guanine, Cytosine and Thymine. Of these adenine and guanine are double-ringed structures called purine and cytosine and thymine are pyrimidine. Uracil on the other hand is present in RNA in the place of thymine and belongs to pyrimidine. Adenime and Thymine forms two hydrogen bond and guanine and Cytosine form three hydrogen bond.