(a) $X(n,\alpha)\ _{3}^{7}Li \Rightarrow \ _{Z}X^{A} + \ _{0}n^{1} \rightarrow 3^{Li^{7}} +_{2}He^{4}$ $Z = 3 + 2 = 5$ and $A = 7 + 4 - 1 = 10$ $\therefore_{5}X^{10} =_{5}B^{10}$
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