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Which notations represent atoms that have the same number of protons but a different number of neutr


Which notations represent atoms that have the same number of protons but a different number of neutrons?

(1) H-3 and He-3

(2) S-32 and S-32

(3) Cl-35 and Cl-37

(4) Ga-70 and Ge-73

Answer and Explanation: Choice 3 is the correct answer choice

Atoms of the same element that have the same number of protons but a different number of neutrons are called isotopes. Whenever we see an element symbol followed by a dash and a number, that number represents the mass of the element. Choice 1 is incorrect since H and He are different elements and therefore have different numbers of protons. Choice 2 is incorrect since these are two identical atoms with the same number of protons and neutrons. Choice 4 is incorrect since Ga and Ge are different elements. Choice 3 is correct since both are atoms of Cl and therefore have the same number of protons. Yet, their masses are different and thus the number of neutrons differ as well.

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