The periodic table
3 marks · Easy(a)[1 mark]
State the number of protons in an atom of magnesium-24.
(b)[1 mark]
State the number of electrons in an atom of magnesium-24.
(c)[1 mark]
Calculate the number of neutrons in magnesium-24.
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(a) 12
(b) 12
(c) 12
Common mistakes: Using mass number as proton/electron number; Incorrect subtraction
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Marking points
A1 (a) · 1 mark · Protons stated as 12.
A2 (b) · 1 mark · Electrons stated as 12.
A3 (c) · 1 mark · Neutrons calculated as 24 - 12 = 12.
Worked solution
a. Magnesium atomic number is 12, so 12 protons.
b. Number of electrons is also 12.
c. Neutrons = mass number - atomic number = 24 - 12 = 12.