Question

The number of electrons lost to convert 6 atoms of A to their stable ions is equal to the number of electrons gained to stabalize 4 atoms of B. If the atomic number of A is 20, what is the charge on the stable ion B?

Answer 1

A is Calcium with atomic number 20. It's stable ion is Ca++. For 6 atoms, 2*6 = 12 electrons are lost.

Thus 12 electrons need to be gained by 4 atoms. Per atom, that's 3 electrons gained. The atom must be then, a group 15 element, say Nitrogen or Phosphorus