Question

One isotope of a metallic element has mass number 10 and has 7 neutrons in the nucleus. It forms an atomic ion having 2 electrons. Enter the symbol for this ion

Answer 1

Mass # 10 means protons + neutrons = 10. If it has 7 neutrons, then protons must be 10-7= 3. Atomic number 3 must be Li. So # electrons in the neutral element must be 3. If the element has just two electrons then the charge of the ion must be +1 so the symbol is Li^1+.