Question

An isotope of a mystery element has 8 protons, 8 electrons, and 10 neutrons. What

is its mass number?

Answer 1

`\boxed {\boxed {\sf D. \ 18 \ amu}}`

Step-by-step explanation:

The mass number is the sum of protons and neutrons.

`mass \ number = \# \ of \ protons + \# \ of \ neutrons`

This mystery element's isotope has 8 protons and 10 neutrons. Protons and neutrons are both equal to 1 amu, so 8 protons is 8 amu and 10 neutrons is 10 amu.

`mass \ number= 8 \ amu +10 \ amu`

Add.

`mass \ number = 18 \ amu`

The mass number of this isotope is 18 atomic mass units.

Answer 2

Fourth Option

Step-by-step explanation:

You find a isotopes mass number by adding the number of protons and neutrons together.

`8+10=18`

Mass Number = 18amu

The mystery element is the element oxygen because oxygen has 8 protons, 8 electrons and 10 neutrons.

Hope this helps.