Multiple Choice
An isotope of sodium (Na) has a mass number of 22. How many neutrons does it have?
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2. Atoms & Elements
Isotopes
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What is the mass number of an atom of potassium that has 20 neutrons?
A
19
B
39
C
20
D
40
Verified step by step guidance1
Identify the atomic number of potassium, which is 19. This represents the number of protons in the atom.
Recall that the mass number of an atom is the sum of its protons and neutrons.
Given that the atom has 20 neutrons, add the number of protons (19) to the number of neutrons (20).
Use the formula: \( \text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons} \).
Substitute the known values into the formula: \( \text{Mass Number} = 19 + 20 \).
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