# An $\alpha$-particle of energy $5 \;MeV$ is scattered through $180^{\circ}$ by a fixed uranium nucleus. The distance of the closest approach is of the order of
( A ) $10^{-12} cm$
( B ) $10^{-10} cm$
( C ) $10^{-15} cm$
( D ) $1\mathring{A}$