Which of the following species correctly represented an ion of M with 13 protons and 10 electrons?

Analyze the question We need the correct symbol for an ion of element M with 13 protons and 10 electrons.

Concept

• The number of protons is the atomic number (Z). It identifies the element and is written as the subscript or, in this question's format, the number beside the symbol.
• Charge = number of protons − number of electrons.
• If protons > electrons, the ion is positive (a cation). If electrons > protons, it is negative (an anion).

Solution

1. Protons = 13, so the atomic number is 13. This is aluminium (Al), written here as M.
2. Charge = 13 − 10 = +3.
3. The ion is therefore M³⁺, with 13 as the number tied to the protons.

Checking the options:

• A and B use 10, which is the electron count, not the proton count, so they are wrong.
• D has the correct 13 but the wrong charge (3−). Having more protons than electrons cannot give a negative ion.
• C shows 13 with a charge of 3+, which is correct.

Answer: C. ¹³M³⁺

(In the question bank's format the 13 is the atomic number. Strictly, the mass number would be larger, about 27 for Al, but the options only test the proton count and the charge.)

Exam tip Use "PEN": Protons − Electrons = Net charge. Positive ions have lost electrons, so Al³⁺ has lost 3 electrons (13 → 10). Metals usually form positive ions.