Sometimes, during the process of replication, the DNA code is copied incorrectly, and an incorrect nucleotide is attached to the new strand of DNA. The type of mutation showed below is called a:a) substitutionb) insertionc) deletiond) translocation

We can see that the original DNA sequence is ATC GTA, with 6 nucleotides.
The incorrect sequence is ATC CTA, also with 6 nucleotides.
Given that the number of nucleotides is the same, this mutation cannot be a deletion or insertion; and as there is only a change of which nucleotide is found in the 4th position, then this mutation is a substitution (a is the right answer)