Answer: loss of electrons
Explanation:
An atom is made up of three subatomic particles named protons neutrons and electrons. An atom forms positive ion with the loss of at least one electron.
For instance: Calcium with atomic number 20, and electronic configuration 1s2, 2s2 2p6, 3s2 3p6, 4s2 will lose the two outermost electrons to form a divalent positive ion (Ca2+).
Ca --> Ca2+ + 2e-
Thus, loss of electrons is the change to an atom that occurs when it forms a positive ion
