A radioactive isotope has the same number of protons as its stable parent atom, but differs in its number of what?

A radioactive isotope has the same number of protons as its stable parent atom, but differs in its number of neutrons.

Explanation:

They have the same number of protons (and electrons), but different numbers of neutrons. These are called isotopes. Different isotopes of the same element have different masses. Isotopes of any given element all contain the same number of protons, so they have the same atomic number Radioactive isotopes are often called radioisotopes. All elements with atomic numbers greater than 83 are radioisotopes meaning that these elements have unstable nuclei and are radioactive.Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. Their nuclei are unstable, so they break down, or decay, and emit radiation.Neutral atoms of an element contain an equal number of protons and electrons. The number of protons determines an element's atomic number (Z) and distinguishes one element from another.

The correct answer would be 1. precipitation