SAT Subject Physics Practice Question 313: Answer and Explanation
9. The symbols used in writing nuclear equations. Atomic nuclei are typically written in the form . Which letter represents the protons plus neutrons in the nucleus?
A. The number of protons is Z.
B. The number of neutrons is X.
C. The symbol of the element is X.
D. The number of electrons is A.
E. The mass number is A.
Correct Answer: E
The correct answer is (E). The number of protons added to the number of neutrons is equal to the mass number of an atom. The mass is represented by the letter A.