## Chemistry: The Molecular Science (5th Edition)

$^{38}_{19}K\rightarrow\,^{38}_{18}Ar+\,^{0}_{1}e$
Let the element that undergoes radioactive decay be $X$, its mass number be $A$ and let the atomic number be $Z$. We know that a positron is a positively charged electron, that is, $^{0}_{1}e$. As argon-38 is formed by positron emission, we can write $^{A}_{Z}X\rightarrow\,^{38}_{18}Ar+\,^{0}_{1}e$ As the sum of masses and charges should be equal on both the sides, we have $A=38+0=38$ $Z=18+1=19$ The element with atomic number $Z=19$ is potassium with the symbol $K$. Therefore, the required balanced nuclear equation is $^{38}_{19}K\rightarrow\,^{38}_{18}Ar+\,^{0}_{1}e$