Question

The mass number of Fe2+ is 56. How many neutrons are there in a single Fe2+ atom?

Answer 1

The atomic number of a neutral atom is equal to the number of protons and the number of electrons of the atom. The atomic weight meanwhile is equal to the sum of the number of protons and number of neutrons. In this case, the number of protons is equal to 26. The number of neutrons hence is 30. 

Answer 2

Answer: the number of neutrons present in a single  $Fe^{2+}$ atom is 30

Explanation: Given atom is $Fe^{2+}$  which is basically ion of iron from which two electrons have been removed .

Thus Atomic number of $Fe^{2+}$ , Z = 26

Mass number of  $Fe^{2+}$ , M=56

Now we know that the mass number of the atom (M) is equal to the sum of the number of protons(P) and neutrons(N) in the nucleus ,i.e., M=P+N ----(A)

Also the number of protons in the nucleus of the atom is equal to the atomic number (Z).

Therefore number of protons , P=Z= 26    

Using equation (A) we get

56=26+ N

=>N=30

Thus the number of neutrons present in a single  $Fe^{2+}$ atom is 30