Why does the atomic number of an isotope remain the same when it undergoes gamma emission?

Gamma ray is a type of low-energy electromagnetic radiation that has a mass but no charge.

Gamma ray is a type of high-energy electromagnetic radiation with no mass and no charge.

Gamma ray is a type of high-energy electromagnetic radiation with a positive electrical charge but with no mass.

Gamma ray is a type of low-energy electromagnetic radiation with a negative electrical charge but with no mass.