Chemistry - Stoichiometry Question with Solution | TestHub

A rock is found to contain $15.2\%{\mathrm{SiO}}_2$ and $10.2\%{\mathrm{Al}}_2{\mathrm{O}}_3$, by mass. Considering that some of ${\mathrm{SiO}}_2$ in rock is present in combined state as Kaolin ( ${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{SiO}}_2$ ) and remaining ${\mathrm{SiO}}_2$ is in free state and ${\mathrm{Al}}_2{\mathrm{O}}_3$ is only in combined state, the percentage of free ${\mathrm{SiO}}_2$ in rock is ( $\mathrm{Al}=27,\mathrm{Si}=28$ )