Multiple Choice
An atom has 4 protons and 5 neutrons. Which element is it?
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4. Atoms and Elements
Isotopes
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Which of the following isotopes is not possible (i.e., would correspond to an element that cannot exist because its atomic number would be 0)?
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Verified step by step guidance1
Understand that an isotope is defined by its number of protons (atomic number) and neutrons (mass number minus atomic number). The atomic number determines the element, and it must be a positive integer greater than zero.
Identify the atomic number for each isotope by looking at the chemical symbol: for example, Hydrogen (H) has atomic number 1, Carbon (C) has atomic number 6, Oxygen (O) has atomic number 8, and a neutron (n) has atomic number 0 because it is not an element but a subatomic particle.
Recognize that an isotope with atomic number 0 would mean it has no protons, which is not possible for an element to exist. A neutron alone is not an element but a particle, so it cannot be considered an isotope of an element.
Check each option: isotopes of Carbon-14, Hydrogen-2, and Oxygen-18 all have valid atomic numbers corresponding to real elements, while 'n¹' represents a neutron with atomic number 0, which is not an element and thus not a possible isotope.
Conclude that the isotope with atomic number 0 (the neutron 'n¹') is not possible as an element, because elements must have at least one proton.
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