(a)(i) Proton number
— the number of protons in the nucleus of an atom
(ii) Nucleon number — the total number of protons and neutrons in the nucleus of are atom.
(iii) Isotopes — are atoms or nuclides of the samc element having the same number of protons or atomic number but different neutrons or mass numbers
(b) ${}_Z^A{\to }_{Z+}^{A}Y{+}_{-1}^0$
${}_{84}^{210}Po{\to }_{82}^{206}Pb{+}_2^{4}He+Energy$
Mass detect = 209.936730u - (205.929421 + 4.001504)u
209.9367330u - 209.930925u
= 5.805 x 10${}^{-3}$U
Energy released = 5.805 x 10${}^{-3}$ x 931
= 5.40MeV