The correct answer is option 1: the monatomic species with 18 electrons and a net charge of 2- has the same number of electrons as a neutral argon atom.
Let`s break down each option to understand why option 1 is the correct answer:
Option 1: The neutral argon atom has 18 electrons. Since the monatomic species also has 18 electrons, these two species have the same number of electrons. Therefore, this option is correct.
Option 2: This option suggests that the monatomic species has more protons than electrons. However, based on the information provided, we know that the species has 18 electrons. Since neutral atoms have the same number of protons as electrons, this option is incorrect.
Option 3: This option states that the monatomic species has 1 unpaired electron. However, we do not have enough information to determine whether this is true or not. Therefore, this option cannot be confirmed or ruled out based on the given information.
Option 4: This option states that the monatomic species has 20 protons. However, there is no information given that indicates this species has 20 protons. Therefore, this option is incorrect.
In conclusion, option 1 is the correct answer