Question

How many neutrons in the `""^56Fe` isotope?

Answer 1

`""^56Fe` has 30 neutrons.

Explanation:

How did I know this? Well, an iron atom has 26 protons, positively charged, massive nuclear particles. The number defines `Z`, the atomic number; `Z=1, H`; `Z=2, He`; `Z=3, Li`;...........`Z=26, Fe`.............

The nucleus also contains neutrons, massive, neutrally charged particles, and to a first approximation, the sum of protons and neutrons gives tha mass of the isotope. So if the question mentions iron, I know that `Z=26`; it is thus simple to specify the isotopic mass if the number of neutrons is given.