Multiple Choice
Which neutral isotope has 17 electrons and 18 neutrons?
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4. Atoms and Elements
Isotopes
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Which element is described by an atom that has 35 protons and 45 neutrons?
A
Krypton (an isotope with mass number )
B
Rubidium (an isotope with mass number )
C
Selenium (an isotope with mass number )
D
Bromine (an isotope with mass number )
Verified step by step guidance1
Identify the element by its number of protons, since the number of protons (also called the atomic number) uniquely defines the element. Here, the atom has 35 protons.
Recall that the atomic number 35 corresponds to the element Bromine (Br) on the periodic table.
Calculate the mass number of the isotope by adding the number of protons and neutrons: \(\text{mass number} = \text{protons} + \text{neutrons}\).
Substitute the given values: \(\text{mass number} = 35 + 45\).
Recognize that this mass number (80) matches the isotope of Bromine, confirming the element and isotope identity.
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