1. An element's most stable ion forms an ionic compound with chlorine having the formula \( \text{XCl}_2 \). If the mass number of the ion is 40 and it has 18 electrons, what is the element and how many neutrons does it have?
(A)Ar, 22 neutrons
(B)Ar, 24 neutrons
(C)S, 24 neutrons
(D)Ca, 20 neutrons
(E)K, 19 neutrons

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