(a)[2]
Insert the missing nuclide in $^{235}_{92}\text{U} \rightarrow \; [\,]\text{Th} + ^4_2\alpha$.
(b(i))[1]
State what nuclear fission means.
(b(ii))[2]
Suggest why thick concrete walls are placed around a nuclear reactor.
(b(iii))[2]
State one environmental advantage and one environmental disadvantage of using a fission reactor to produce electrical energy in a power station.
(c)[3]
Calculate how many atoms in this sample decay during the next $52\,\text{hours}$.