SAT Subject Physics Practice Question 292: Answer and Explanation

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Question: 292

63. An atom whose nucleus contains 17 protons and 20 neutrons is a chlorine atom. Which of the following describes the composition of the nucleus of an isotope of chlorine?

A. 20 protons, 17 neutrons
B. 19 protons, 18 neutrons
C. 18 protons, 18 neutrons
D. 17 protons, 19 neutrons
E. 16 protons, 20 neutrons

Correct Answer: D


Isotopes of an element contain the same number of protons but different numbers of neutrons. So any isotope of chlorine must contain 17 protons.

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