Natom contains 70 protons, 70 electrons, and 99 neutrons. what is the mass number?

Answer is. mass number of atom N is 169.
e⁻ = 70; number of electrons.
p⁺ = 70, number of protons.
n° = 99; number of neutrons.
A = ?, mass number or atomic mass.
The mass number A is sum of the number of protons and the number of neutrons in atom.
A = n° + p⁺.
A = 99 + 70.
A = 169.