is member of actinium series. Another member of the same series is — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

The actinium series follows the mass number formula $4n + 3$. For ${}_{84}\text{Rn}^{219}$, $219 = 4(54) + 3$. Checking the options, ${}_{92}\text{U}^{235}$ has mass $235 = 4(58) + 3$, which also belongs to the $4n+3$ series. The others do not fit this mass requirement or are light elements. Therefore, correct answer is A.