Assuming that only particles emitted during natural radioactive decay are alpha and beta particles, — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Natural decay sequences involve changes in mass number only by multiples of 4 (due to alpha particles). To form ${}_{89}\text{Ac}^{235}$ from ${}_{92}\text{U}^{235}$, the mass number must remain the same (zero alpha decays). This would require 3 positron emissions or electron captures to reduce the atomic number by 3, but the question specifies only alpha and beta ($\beta^-$) particles are emitted. Standard beta emission would increase, not decrease, the atomic number. Therefore, correct answer is C.