(a(i))[2]
Calculate how many neutrons are in one strontium-90 nucleus.
(a(ii))[1]
Determine the number of electrons in one strontium-90 atom.
(b)[1]
Describe what $\beta$-particles are like.
(c)[2]
Calculate the time needed for the strontium-90 to decay until just 2.0 mg of strontium-90 is left in the sample.