ATGC ATC isn't this substitution

The correct answer would be a deletion mutation.

Deletion mutation is a type of mutation in which a sequence of DNA gets lost during the replication process.

The length of a lost sequence may vary from a single nucleotide to the entire length of a chromosome.

It can also be caused by errors during crossing over that takes place in meiosis I.

A deletion that does not occur in multiples of three nucleotides can result in frame-shift mutation.

Similarly, in the given sequence ATGC, guanine is deleted which results in the formation of a new reading frame that is, ATC.