Answer: C. The nuclear radius relation is $R=R_0A^{1/3}$ From the figure, $R_X/R_Y=(8/64)^{1/3}=1/2$ The mass ratio is $1/8$ and the spherical volume ratio is $(1/2)^3=1/8$ so $\rho_X/\rho_Y=(1/8)/(1/8)=1$

A: uses the mass ratio as the density ratio, omitting the volume comparison.
B: reverses the radius ratio, although its density ratio is unity.
D: treats the masses as equal and uses the inverse volume ratio, giving $8$
Remember: nuclear mass and volume both scale with nucleon number, so nuclear density is constant.