(b) Since, 8$\alpha - particles\ \ 4\beta$$^{—}$particles are emitted, and $2\beta$$^{+}$ particles are emitted so new atomic number.
$Z’ = \ Z - 8\ \times \ 2\ + \ 4\ \times 1\ - \ 2 \times 1$
$= 92 - 16\ + \ 4 - 2$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 92 - 14$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 78$