Multiple Choice
Which number on the periodic table represents the atomic mass of an element?
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2. Atoms & Elements
Atomic Mass
Struggling with General Chemistry?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
What is the mass number of a potassium (K) atom that has 20 neutrons?
A
39
B
40
C
20
D
19
Verified step by step guidance1
Recall that the mass number (A) of an atom is the sum of the number of protons (Z) and neutrons (N) in its nucleus. This can be expressed as: \(A = Z + N\).
Identify the atomic number (Z) of potassium (K), which is the number of protons. For potassium, \(Z = 19\).
Use the given number of neutrons, which is \(N = 20\) in this problem.
Substitute the values into the mass number formula: \(A = 19 + 20\).
Add the numbers to find the mass number of the potassium atom.
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