How many base pairs would a dna segment of length 1.36mm have?

4.0 million

Explanation:

The average length of a base pair (bp) is 340 pm (340 × 10^-12 m)

Length of DNA = Number of bp × length of each bp

 1.36 × 10^-3 m = bp × 340 × 10^-12 m

                    bp = (1.36 × 10^ -3)/(340 × 10^-12)  = 4.0 × 10^6

The DNA segment would contain 4.0 million bp.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.