An ion has a charge of -1 . It has eighteen electrons and twenty neutrons. Its mass number is

X has 18 electrons with a net charge of -1 which means it gained one electron. Hence no. of protons is (18−1=)17. So the atomic no. will be 17. X has 20 neutrons. Mass no. is the addition of protons and neutrons so the mass no. will be 37.

Its symbol will be ¹⁷X₃₇