  The effects of neutron skin on the multiplicity ($N_{\rm ch}$) and elliptic
flow ($v_2$) in relativistic $^{96}_{44}$Ru+$^{96}_{44}$Ru and
$^{96}_{40}$Zr+$^{96}_{40}$Zr collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV are
investigated with the Trento model. It is found that the Ru+Ru/Zr+Zr ratios of
the $N_{\rm ch}$ distributions and $v_2$ in mid-central collisions are
exquisitely sensitive to the neutron skin type (skin vs. halo). The
state-of-the-art calculations by energy density functional theory (DFT) favor
the halo-type neutron skin and can soon be confronted by experimental data. It
is demonstrated that the halo-type density can serve as a good surrogate for
the DFT density, and thus can be efficiently employed to probe nuclear
deformities by using $v_2$ data in central collisions. We provide hereby a
proof-of-principle venue to simultaneously determine the neutron skin type,
thickness, and nuclear deformity.
