A guanine-cytosine base pair contains three hydrogen bonds. In DNA, guanine, abbreviated G, pairs specifically with cytosine, abbreviated C, and their matching chemical groups form three hydrogen bonds across the space between the two strands.
This is part of complementary base pairing, the rule that makes DNA’s two strands useful templates for one another. Adenine pairs with thymine through two hydrogen bonds, while guanine pairs with cytosine through three. The pairing is precise because the bases’ shapes and hydrogen-bonding groups fit together.
The three bonds are often associated with greater stability, so DNA regions rich in G-C pairs generally require more heat to separate than regions rich in A-T pairs. However, hydrogen bonds are not the whole explanation: base-stacking interactions between neighboring bases also make a substantial contribution to DNA stability.
A common mistake is to count the bonds connecting the phosphate-sugar backbone. Those are covalent phosphodiester bonds, not hydrogen bonds. The three hydrogen bonds in this question occur specifically between the paired guanine and cytosine bases.