SAT Subject Physics Practice Question 665: Answer and Explanation
1. What is the one factor that distinguishes each element from every other element?
A. The number of protons in the nucleus
B. The number of neutrons in the nucleus
C. The number of electrons about the nucleus
D. The total mass of the nucleus (protons plus neutrons)
E. Its position on the periodic table
Correct Answer: A
The correct answer is (A). The only single factor that makes each element unique is the number of protons the element has in its nucleus.