Answer:
Base pairs occur when nitrogenous bases make hydrogen bonds with each other. Each base has a specific partner: guanine with cytosine, adenine with thymine (in DNA) or adenine with uracil (in RNA). The hydrogen bonds are weak, allowing DNA to 'unzip'.
The bases which pair with each other are
Guanine - Cytosine
Adenine - thymine(DNA), uracil acid(RNA)
Guanine and Cytosine make three hydrogen bonds
Adenine and thymine/uracil acid make two hydrogen bonds
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