Question detail
A sodium ion (Na+) has an atomic number of 11 and a mass number of 23. How many electrons does it have?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atomic structure
Question
- A. 11
- B. 10
- C. 12
- D. 23
Answer
10
Explanation
The atomic number (11) indicates the number of protons. A sodium ion (Na+) has lost one electron, so the number of electrons is 11 - 1 = 10.
Common mistake
Misidentifying Neutrons from Mass Number
Students often subtract the atomic number from the mass number to find the number of neutrons, but then forget to adjust for the ion’s charge when calculating electrons.
Remember that the number of neutrons is always mass number minus atomic number, independent of charge. The electron count is atomic number minus the ion’s charge (negative charge means +1 electron, positive charge means –1 electron).
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