Bauxite is leached with:

Bauxite is leached with NaOH.

By leaching bauxite with a concentrated NaOH solution, sodium aluminate and sodium silicate are produced. When bauxite (powdered ore) is treated with concentrated NaOH during the metallurgy of aluminum, sodium aluminate $\left(\mathrm{Na}\left[\mathrm{Al}\left({\mathrm{OH}}_4\right]\right)\right.$ is produced, and the impurity (${\mathrm{SiO}}_2$) contained in the bauxite dissolves by creating sodium silicate $\left({\mathrm{Na}}_2{\mathrm{SiO}}_3\right)$.

Hence, option C is correct.