Ion identification reveals atomic number

Steps:

• Examine the diagram to identify the ion as Na⁺ (sodium ion).
• Recall that the atomic number of sodium is 11.
• Understand that the number of protons equals the atomic number for any atom or ion of that element.
• Conclude the ion has 11 protons, as the charge indicates lost electrons but not changed protons.

Why C is correct:

• The number of protons defines the element's atomic number, which is 11 for sodium (Na), as shown in the diagram.

Why the others are wrong:

• A is incorrect; 9 protons correspond to fluorine (F), not the diagrammed ion.
• B is incorrect; 10 protons correspond to neon (Ne), a neutral noble gas, not this ion.
• D is incorrect; the diagram specifies the element, allowing deduction of protons.

Final answer: C