The 41 beside the chemical symbol of calcium signifies the mass number of the isotope which would be 41. It would be equal to the sum of the number of protons and neutrons in the atom. The number of proton is equal to every isotope calcium has which is 20. Therefore, the number of neutrons would be 21. Since it is being stated that the atom is neutral, the number of electrons would be equal to protons which is 20.
