# The mass number of common krypton is 84, and its atomic number is 36. krypton-84 has how many neutrons within each isotope?

Jun 23, 2016

$\text{48 neutrons}$

#### Explanation:

The mass number, $A$, of a given isotope tells you the number of protons, $Z$, which is given by the atomic number, and neutrons it has in its nucleus.

$\textcolor{b l u e}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} A = Z + \text{no. of neutrons} \textcolor{w h i t e}{\frac{a}{a}} |}}}$

In your case, krypton-84 is said to have a mass number equal to

$A = 84$

This means that the nucleus of a krypton-84 isotope contains a total of $84$ protons and neutrons.

Since the element has an atomic number equal to $36$, it follows that it will contain $36$ protons in its nucleus. Therefore, the number of neutrons present in the nucleus of a krypton-84 isotope will be

$\text{no. of neutrons} = A - Z$

$\text{no. of neutrons} = 84 - 36 = \textcolor{g r e e n}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{48} \textcolor{w h i t e}{\frac{a}{a}} |}}}$