Answer
$0.02\%$
Work Step by Step
Mass of water= $density \times volume$
$=\frac{1.00\,g}{mL}\times1.00\,L$
$=\frac{1.00\,g}{10^{-3}\,L}\times1.00\,L=1000\,g$
Mass fraction of $NaHCO_{3}$
$=\frac{mass\,of\,NaHCO_{3}}{mass\,of\,all\,solutes\,and\,the\,solvent}$
= $\frac{0.20\,g}{6.5\,g+0.20\,g+0.10\,g+0.10\,g+1000\,g}= 0.0002$
Weight percent= $mass\, fraction\times100\%$
$= 0.0002\times100\%=0.02\%$
