A nucleus 84 X 202 of an element emits an alpha particle followed by a beta particle. The final nucleus is a Y b . Find a and b.

The emission of alpha and beta particle is represented below:

$$\begin{aligned}_{84}^{202}\text{X} \longrightarrow \space _{82}^{198}\text{Z} + \space _{2}^{4}\text{He} \text{ (α particle emission)} \\[2em] _{82}^{198}\text{Z} \longrightarrow \space _{83}^{198}\text{Y} + \space _{-1}^{\space \space \space 0}e \text{ (β particle emission)}\end{aligned}$$

∴ a = 83 and b = 198