An ionic compound is expected to have a tetrahedral structure if $r_{\mathrm{c}}/r_{\mathrm{a}}$

An ionic compound is expected to have a tetrahedral structure if $r_{\mathrm{c}}/r_{\mathrm{a}}$ is lies in the range of 0.225 to 0.414

When there are four bonds and no lone pairs in the core atom of the molecule, the molecule is said to be tetrahedral. With 109.5° angles between them, the atoms that are bound to the core atom are positioned at its four corners.

The ratio is found  as

 $0.225 >\frac{r_c}{r_a}>0.414$

Hence option C is correct