Question

One isotope of sodium has 11 protons and 7 neutrons. What is the mass number of this isotope? Which property of the isotopes must be different?

Answer 1

18 is the mass number(total number of protons and neutrons in a nucleus). To differentiate between isotopes, you must look at the number of neutrons. This is what makes an isotope different from another.

Hope this helps!

Answer 2

18

Step-by-step explanation:

The mass number of an isotope could be calculated using the following equation;

`A=N_p+N_n................(1)`

where A represents the mass number,
`N_p` represents the number of protons and
`N_n` represents the number of electrons.

Given;

`N_p=11\\N_n=18\\hence\\A=11+7\\A=18`

isotopes are defined generally as two or more atoms of the same element having the same atomic number but different mass numbers.

Hence the property that differs in isotopes is their mass numbers.