Concentrated nitric acid used in laboratory work is 68% nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the nitric acid, if the density of the solution is 1.504 g mL^-1 ?

$68\mathrm{\%}{\mathrm{HNO}}_3 \mathrm{means}$
68 g of nitric acid in 100 g solution.
Density of the solution= 1.504 g mL^-1
$\text{ Moles of }{\mathrm{HNO}}_3=\frac{68}{63}=1.079\mathrm{mol}$
         $\left[\because {\mathrm{HNO}}_3=1+14+16\times 3=63\mathrm{g}{\mathrm{mol}}^{-1}\right]$
$\text{ Volume of the solution }=\frac{100}{1.504}=66.5\mathrm{mL}=0.0665\mathrm{L}$
$\text{ Molarity of the solution }=\frac{1.079}{0.0665}=16.23\mathrm{M}$