Question

Atomic nuclei are typically written in the form ${}_Z^{A}X$. Identify 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 $A$

Answer 1

Answer: (E)

The mass number is $A$

The nuclei ${}_Z^{A}X$ indicates it has mass number $=A$ and protons or electrons number $=Z$ and neutrons number $N=A-Z$.

Thus, $A=N+Z$