The total number of neutrons in di positive zinc ions with mass number 70 is:

The total number of neutrons in di positive zinc ions with mass number 70 is: 40.

Protons and neutrons together make up mass.
Protons or electrons make up an atom's atomic number.
Zinc has 30 electrons and has an atomic number of 30. 28 electrons are present since 2 electrons are lost in dipositive ions.
Mass number = 70 
Mass = 70 = 30 + number of neutrons
So, the 70 mass zinc ion has 40 neutrons, which equals the number of neutrons.

Hence, option B is correct.