If `M` is atomic weight, `A` is mass number then `(M-A)//A` represents

An element M has an atomic number 9 and mass number 19. Its ion will be represented by (1) M (2) M^(2+) (3) M^(-) (4) M^(2-)

An element M has atomic mass 19 and atomic number 9 . Its ion is represented as

An ion M^(2+) contains 10 electrons and 12 neutrons .What is the atomic number and mass number the element M? Name the element.