Answer
3.4 g $NaHCO_{3}$
Work Step by Step
Molarity M= 0.20 M
Volume of solution in litre V= 0.200 L
Number of moles of solute n=MV=$0.20\,M\times.200\,L= 0.040\, mol$
Mass in grams= n$\times$ Molar mass of $NaHCO_{3}$
$= 0.040\,mol\times84.0\, g/mol=3.4\, g$