Multiple Choice
Which formula represents a hydronium ion?
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2. Atoms & Elements
Ions
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Which of the following is the correct symbol for the ion with 19 protons and 18 electrons?
A
K^+
B
K^-
C
K^{2+}
D
K
Verified step by step guidance1
Identify the element by its number of protons. The number of protons defines the atomic number, which determines the element. Here, the ion has 19 protons, so the element is potassium (K), since potassium has atomic number 19.
Determine the charge of the ion by comparing the number of protons and electrons. The ion has 19 protons (positive charges) and 18 electrons (negative charges). Since there is one fewer electron than protons, the ion has a net positive charge of +1.
Write the symbol for the ion by placing the element symbol (K) followed by the charge as a superscript. Since the charge is +1, the correct notation is $K^{+}$.
Verify that the other options do not match the charge: $K^{-}$ indicates one extra electron (negative charge), $K^{2+}$ indicates two fewer electrons (charge +2), and $K$ without a charge indicates a neutral atom with equal protons and electrons.
Conclude that the correct symbol for the ion with 19 protons and 18 electrons is $K^{+}$.
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