1) Answer is: This ion is Br⁻ (bromine anion).
This ion has 36 electrons, because it has charge -1 (atom gain one electron), its atom has 35 electrons and 35 protons (atomic number 35). Element with atomic number 35 is bromine.
Electron configuration of ion with a charge of -1: ₃₅Br⁻ 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶.
2) Answer is: chemical symbol of the noble gas is Kr (krypton).
Isoelectronic atom or ion has the same number of valence electrons. Krypton has 36 electron and 36 protons (atomic number 36).
Isoelectronic species are species with same number of electrons.
The given electronic configuration of the ion is as follows:
[tex]1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}[/tex]
Check for the total number of electrons in the ion. The sum of number of electrons in all shells according to given electronic configuration is 36. Number of electrons in a neutral atom is equal its atomic number. According to periodic table, atomic number of krypton is 36, which is a noble gas and belongs to 18th group with electronic symbol Kr. It has the same electronic configuration thus, it is isoelectronic with the ion.
Therefore, the chemical symbol for noble gas isoelectronic with the given ion is Kr.
