Which change in DNA was a point mutation?

These external agents of genetic change are called mutagens. Exposure to mutagens often causes alterations in the molecular structure of nucleotides, ultimately causing substitutions, insertions, and deletions in the DNA sequence.

Explanation: Point mutations are a large category of mutations that describe a change in single nucleotide of DNA, such that that nucleotide is switched for another nucleotide, or that nucleotide is deleted, or a single nucleotide is inserted into the DNA that causes that DNA to be different from the normal or wild type gene