Multiple Choice
Which element is described by an atom that has 35 protons and 45 neutrons?
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4. Atoms and Elements
Isotopes
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An atom has 18 protons and 22 neutrons. Which element is it, and what is its mass number?
A
Chlorine, mass number
B
Argon, mass number
C
Calcium, mass number
D
Argon, mass number
Verified step by step guidance1
Identify the element by the number of protons. The number of protons in an atom is called the atomic number, which determines the element's identity. Here, the atom has 18 protons.
Use the periodic table to find the element with atomic number 18. This element is Argon (Ar).
Calculate the mass number of the atom. The mass number is the sum of protons and neutrons in the nucleus.
Add the number of protons (18) and neutrons (22) to find the mass number: \$18 + 22$.
Conclude that the element is Argon with a mass number equal to the sum calculated in the previous step.
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