An ionic compound is expected to have an octahedral structure if $r_{\mathrm{c}}/r_{\mathrm{a}}$ lies in the range of

An ionic compound is expected to have an octahedral structure if $r_{\mathrm{c}}/r_{\mathrm{a}}$ lies in the range of 0.414 to 0.732

Octahedral molecular geometry, also known as square bipyramidal, describes compounds that have six atoms, groups of atoms, or ligands symmetrically arranged around a centre atom, creating the vertices of an octahedron.

The ratio is found  as

 $0.414 >\frac{r_c}{r_a}>0.732$

Hence option A is correct