The molarity of the solution containing $2.8\%$ (mass / volume) solution of $\mathrm{KOH}$ is : (Given atomic mass of $\mathrm{K}=39$) is :

$500\mathrm{mL}$ of a glucose solution contains $6.02\times {10}^{22}$ molecules. The concentration of the solution is;

$1.5 \mathrm{g}$ mixture of ${\mathrm{SiO}}_2$ and ${\mathrm{Fe}}_2{\mathrm{O}}_3$ on very strong heating leave a residue weighing $1.46 \mathrm{g}.$ The reaction responsible for loss of weight is

${\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)\to {\mathrm{Fe}}_3{\mathrm{O}}_4\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$

What is the percentage by mass of ${\mathrm{Fe}}_2{\mathrm{O}}_3$ in original sample.