A monoatomic ion with a mass number of 56 contains 3 units of positive charge and exactly $30.4\%$ m

Question

A monoatomic ion with a mass number of 56 contains 3 units of positive charge and exactly $30.4\%$ more neutrons than electrons. The correct symbol of this ion is

Professor PC Thomas Classes · Answer

(a) : Let the number of electrons in the ion be $e$. Since it carries a $+3$ charge, the number of protons $p = e + 3$. The number of neutrons $n$ is $30.4\%$ more than the electrons, so $n = e + 0.304e = 1.304e$. The mass number $A = p + n = 56$. Therefore, $(e + 3) + 1.304e = 56 \implies 2.304e = 53 \implies e = \frac{53}{2.304} = 23$. The number of protons is $p = 23 + 3 = 26$, which identifies the element as Iron ($\mathrm{Fe}$). The ion is ${}^{56}_{26}\mathrm{Fe}^{3+}$.