Question

A neutral atom possesses an atomic number of 13 and an atomic mass of 27. Three electrons are lost. From what region of the atom are they lost?

Answer 1

From the outer or highest energy shell.

The atomic number 13 implies this electronic configuration 1 s2 2s2 2p6 3s2 3p1.

There are three electrons in the outer shell (3s2 3p1)which are those that the atom can loose more easily (precisely for having the higher energy or being farther from the nucleus)

Answer 2

The outside shell where the electrons orbit.