Find out the number of electrons present in the last shell of an atom having atomic number 15.

The atomic number of the atom = 15

Number of protons = 15

A number of electrons = 15 because the atom is neutral.

So representing the electrons by electronic configuration,

K = 2 electrons

L = 8 electrons

M = 5 electrons

The M shell has 5 electrons and it is the last shell of the atom, so the number of the electrons in the last shell of an atom with atomic number 15 is 5.