A hypothetical ceramic, Marylandium Oxide $($MdO$),$ has a $3\mathrm{.}5$ g$/$cm$3$ density and

a cubic unit cell with a cell edge length of $0\mathrm{.}396$ nm$.$ The Md and O atomic weights are $19\mathrm{.}9$ and $13\mathrm{.}0$ g$/$mol$,$ respectively.

a$)$ Draw the arrangement for the ions on the $(110)$ plane, showing where the ions touch $($if they touch$)$ in the MdO structure. Mark all close$-$packed directions and label them with the appropriate Miller$-$Bravais directional indices.