Multiple Choice
Which element is described by an atom that has 19 protons and 20 neutrons?
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4. Atoms and Elements
Isotopes
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In atomic structure, how is the mass number of an atom calculated?
A
It is the same as the atomic number (the number of protons).
B
It is the sum of the number of protons and neutrons in the nucleus.
C
It is the sum of the number of protons and electrons in the atom.
D
It is the difference between the number of neutrons and protons in the nucleus.
Verified step by step guidance1
Understand that the mass number of an atom represents the total count of the particles that contribute most of the atom's mass, which are protons and neutrons located in the nucleus.
Recall that the atomic number is the number of protons in the nucleus, which defines the element but does not account for the total mass.
Recognize that electrons have negligible mass compared to protons and neutrons, so they are not included in the mass number calculation.
Use the formula for mass number: \(\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}\).
Therefore, to find the mass number, add the number of protons and neutrons together, which gives the total mass of the nucleus.
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