First measurements of the branching fractions of $ J/\psi \to {\mathrm{\Xi }}^{0}\overline{\mathrm{\Lambda }}{K}_{S}^{0}+c.c.$, $ J/\psi \to {\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{0}{K}_{S}^{0}+c.c.$, and $ J/\psi \to {\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{-}{K}^{+}+c.c.$

By analyzing $ (10087\pm 44)\times {10}^{6}J/\psi $ events collected with the BESIII detector at the BEPCII, the decays $ J/\psi \to {\mathrm{\Xi }}^{0}\overline{\mathrm{\Lambda }}{K}_{S}^{0}+c.c.$, $ J/\psi \to {\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{0}{K}_{S}^{0}+c.c.$, and $ J/\psi \to {\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{-}{K}^{+}+c.c.$ are observed for the first time. Their branching fractions are determined to be $ \mathcal{B}(J/\psi \to {\mathrm{\Xi }}^{0}\overline{\mathrm{\Lambda }}{K}_{S}^{0}+c.c.)=\phantom{\rule{0ex}{0ex}}(3.76\pm 0.14\pm 0.23)\times {10}^{-5}$, $ \mathcal{B}(J/\psi \to {\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{0}{K}_{S}^{0}+c.c.)=(2.24\pm 0.32\pm 0.31)\times {10}^{-5}$, and $ \mathcal{B}(J/\psi \to \phantom{\rule{0ex}{0ex}}{\mathrm{\Xi }}^{0}{\overline{\mathrm{\Sigma }}}^{-}{K}^{+}+c.c.)=(5.64\pm 0.17\pm 0.28)\times {10}^{-5}$, where the first uncertainties are statistical and the second systematic.