Question

what is a substitution mutation?
○ the addition of one or more nucleotide pairs to a dna molecule
○ the exchange of one nucleotide for another nucleotide in mrna
○ the removal of one or more nucleotide pairs in a dna molecule
○ the exchange of one nucleotide for another nucleotide in a dna molecule

Explanation:

A substitution mutation specifically involves swapping one nucleotide for another within the DNA molecule. The first option describes an insertion mutation (adding nucleotides), the second is incorrect as substitution mutations occur in DNA not mRNA, the third is a deletion mutation (removing nucleotides). So the correct description is the exchange of one nucleotide for another in a DNA molecule.

Answer:

the exchange of one nucleotide for another nucleotide in a DNA molecule