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Multiple Choice
Which of the following cations will form an ionic compound with the formula X(NO3)2, where X is the cation and two nitrate ions are present?
A
K^{+}
B
Al^{3+}
C
Mg^{2+}
D
Na^{+}
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1
Identify the charge on the nitrate ion, NO3^-, which is -1.
Since the formula is X(NO3)2, there are two nitrate ions, contributing a total charge of 2 × (-1) = -2.
For the compound to be electrically neutral, the cation X must have a charge of +2 to balance the -2 charge from the nitrate ions.
Examine the charges of the given cations: K^{+} has +1, Al^{3+} has +3, Mg^{2+} has +2, and Na^{+} has +1.
Select the cation with a +2 charge, which is Mg^{2+}, because it balances the two nitrate ions to form a neutral ionic compound with the formula X(NO3)2.