Write the symbol for the monatomic ion that has a charge of 1– and the condensed electron configuration [ne]3s23p6.

Answer is: the symbol is Cl.
[Ne ] 3s² 3p⁶ is electric configuration of noble gas argon, neon (Ne) has10 electrons plus 6 electrons in 3s and 3p orbitals. Neutral atom of monatomic ion that has a charge of 1– has one electron less than argon, so that atom (chlorine) has 17 electrons. Charge of 1- means one electron more for ion: 17 + 1 = 18.

Answer is to avoid experimental error