An yttrium isotope has 39 protons and 50 neutrons in its nucleus. Which one of the following symbols accurately represents this isotope?

Question

Quizplus · Accepted Answer

The correct symbol for an isotope is given by ${ }_{Z}^{A}\mathrm{X}$, where $Z$ is the atomic number (number of protons), $A$ is the mass number (sum of protons and neutrons), and $X$ is the chemical symbol. For an yttrium isotope with 39 protons and 50 neutrons, $A = 39 + 50 = 89$, and since yttrium's atomic number ($Z$) is 39, the correct symbol is ${ }_{39}^{89}\mathrm{Y}$.

An Yttrium Isotope Has 39 Protons and 50 Neutrons in Its