SAT Subject Physics Practice Question 486: Answer and Explanation

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Question: 486


A radium atom decays into a radon atom as shown in the equation above. Which of the quantities below correctly finishes the equation?

A. Alpha
B. Beta
C. Gamma
D. Neutron
E. Neutrino

Correct Answer: A


The correct answer is (A). The mass numbers of the reactants and products must be the same, a mass value of 4 is missing on the product side. Likewise the atomic number on both sides of the equation must be the same. A value of 2 is missing on the product side, leaving (a mass number of 4, and an atomic number of 2 as the missing value). This is an alpha particle or .

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