(b) $\ _{88}A^{196} \rightarrow \ _{78}B^{164}$
Number of $\alpha - particles$ $= \ \frac{196 - 164}{4}\ = 8$
$\ \ \ \ \ \ \ \ \ \ \ _{88}A^{196}\overset{- 8\alpha\ \ \ \ \ }{\rightarrow}\ _{72}X^{164} \rightarrow \ _{78}B^{164}$
$\therefore$ Number of $\beta - particles$ =$78 - 72 = 6$