SAT Subject Physics Practice Question 146: Answer and Explanation

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Question: 146

9. What’s the missing particle in the following nuclear reaction?

A. Proton
B. Neutron
C. Electron
D. Positron
E. Deuteron

Correct Answer: B

Explanation:

In order to balance the mass number (the superscripts), we must have 2 + 63 = 64 + A, so A = 1. In order to balance the charge (the subscripts), we need 1 + 29 = 30 + Z, so Z = 0. A particle with a mass number of 1 and no charge is a neutron, .

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