Question detail
If an ion has an atomic number of 20, a mass number of 40, and a charge of +2, 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
A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes
Question
- A. 20 electrons
- B. 18 electrons
- C. 22 electrons
- D. 40 electrons
Answer
18 electrons
Explanation
The ion has lost 2 electrons due to its +2 charge, so it has 20 - 2 = 18 electrons.
Common mistake
Confusing Protons and Neutrons
Students often confuse the number of protons with the number of neutrons when calculating the composition of an atom.
Remember that the atomic number represents the number of protons, while the mass number is the total of protons and neutrons. Use the formula: Neutrons = Mass Number - Atomic Number. Keep the correction anchored to Size and mass of atoms and avoid mixing it with nearby Unit 4.1 ideas.
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