Question

${}_{92}{U}^{238}$ changes to ${}_{85}{U}^{210}$ by a series of $\alpha$ and $\beta$ decays. Find the number of $\alpha$ decays undergone (an integer)

Answer 1

For $\alpha$ decay: $X_Z^A\to Y_{Z-2}^{A-4}$
For $\beta$ deacy: $X_Z^A\to Y_{Z+1}^A$
Thus, number of $\alpha$ decays $=\frac{238-210}{4}=\frac{28}{4}=7$