Question

If an element has atomic number 9 and atomic mass 19, how many neutrons will it have?

Answer 1

TEN neutrons.........

Explanation:

To an excellent approximation, atomic mass is equivalent to nuclear mass; i.e. the combined mass of neutrons and protons. Can you tell us the identity of the nuclide? You have all the info necessary to do so.

Answer 2

10 neutrons.

Explanation:

We know that Mass number `~~` Atomic mass of an atom(as electrons weigh almost nothing relative to an atom, although each of them have mass of `9.11 * 10^-34` kg. );
Mass Number = Number of Protons + Number of Neutrons;
And Atomic Number = Number of Protons.

So Number of Neutrons = Atomic Mass - Atomic Number = 19 - 9 = 10
This explains the answer.