Which of the following is most likely responsible for this mutation

Mutations occur due to various causes.

DNA fails to copy accurately

Most of the mutations that we think are important for evolution happen naturally. For example, when a cell divides it makes a copy of its DNA and, sometimes, that copy is not perfect. That small difference with the original DNA sequence is a mutation.

Radioactive signs Mutations can also be caused by exposure to chemicals or radiation. These agents cause the degradation of DNA. This is not determined unnatural, since DNA degrades even in the most isolated and immaculate environments. However, when the cell repairs the DNA, it may not make a perfect repair, so the cell ends with a slightly different DNA from the original and, therefore, with a mutation.