How can i find out the number of neutrons in an atom ?

Answer 1

The atomic number ,denoted by Z represents the number of electrons in the atom.The mass number A represents the number of nucleons i.e.protons and neutrons.
A=Z+N
N=A-Z
where N represents the number of neutrons in the atom.
Therefore the number of neutrons is obtained by subtracting atomic number from mass number.

Answer 2

The number of neutrons N + the number of protons Z = A number of mass. In tne periodic table, you find A and Z . Then to find N substract N = A-Z

Ex Fluorine on my link you find Z=9 A=19 so N= 19-9=10 neutrons