Which nitrogenous bases pair with each other? What type of hydrogen bond forms between them?

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

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'.