Answer
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Work Step by Step
The element with 18 neutrons is oxygen (O) and the element with 20 neutrons is neon (Ne). Since the element forms 1- charged ions in ionic compounds, it means that the element gains one electron to achieve a stable electron configuration.
For oxygen (O), which has 8 protons and 8 electrons in a neutral atom, it will gain one electron to form a 1- charged ion with 9 electrons.
Therefore, the 1- charged ion of the element in this case has 9 electrons.
