Which component of a DNA synthesis reaction determines the exact nucleotide sequence of the product?

The complementary base pairing between incoming nucleotides and the DNA template

Explanation:

In a DNA synthesis reaction, the exact nucleotide sequence of the product is basically determined by both the DNA template from which a new strand is made and the incoming new nucleotides that makes up the new DNA strands. A complementary base Paris between these two gives the nucleotide sequence of the product.