The periodic table
2 marks · NormalState the number of protons and the number of neutrons in an atom of phosphorus-31.
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15 protons, 16 neutrons
Also accept: protons: 15, neutrons: 16; 15 and 16 respectively
Common mistakes: 16 protons, 15 neutrons; Using mass number for protons
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Marking points
B1 · 1 mark · State the correct number of protons (15)
B2 · 1 mark · State the correct number of neutrons (16)
Worked solution
The atomic number of phosphorus is 15, so it has 15 protons.