Multiple Choice
How many neutrons are in a atom?
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4. Atoms and Elements
Isotopes
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Argon’s most abundant isotope is argon-40. How many neutrons are in one atom of ?
A
58
B
18
C
40
D
22
Verified step by step guidance1
Identify the atomic number and the mass number from the isotope notation. The atomic number (number of protons) is the subscript, and the mass number (total number of protons and neutrons) is the superscript. For argon-40, the atomic number is 18 and the mass number is 40.
Recall that the number of neutrons in an atom is calculated by subtracting the atomic number from the mass number.
Write the formula for the number of neutrons: \(\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}\).
Substitute the values for argon-40 into the formula: \(\text{Number of neutrons} = 40 - 18\).
Perform the subtraction to find the number of neutrons in one atom of argon-40.
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