Answer
Please see the work below.
Work Step by Step
We know that
$Bi^{209}_{83}+He^{2}_{1}\rightarrow Po^{A}_{84}+n^{1}_{0}$
From the superscripts, we obtain:
$209+2=A+1$ so $A=211-1=210$
The required reaction is
$Bi^{209}_{83}+He^{2}_{1}\rightarrow Po^{210}_{84}+n^{1}_{0}$
