Multiple Choice
An atom has an atomic number of 15 and a mass number of 31. How many protons are present in this atom?
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2. Atoms & Elements
The Atom
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Astatine has 85 protons. What is its atomic number?
A
85
B
127
C
53
D
210
Verified step by step guidance1
Recall that the atomic number of an element is defined as the number of protons in the nucleus of an atom of that element.
Identify the number of protons given in the problem, which is 85 for astatine.
Since the atomic number equals the number of protons, the atomic number of astatine is therefore 85.
Understand that the atomic number uniquely identifies an element on the periodic table, so astatine's atomic number 85 places it in the correct position.
Confirm that the other numbers given (127, 53, 210) do not correspond to the atomic number but could represent other properties such as mass number or unrelated values.
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