Molar mass sucrose :
C12H22O11 = 342.29 g/mol
number of moles of the solute :
n = mass solute / molar mass
n = 17.1 / 342.29
n = 0.05 moles
Volume in liters :
250 mL / 1000 = 0.25 L
therefore :
Molarity = moles of solute / volume
Molarity = 0.05 / 0.25 => 0.2 mol/L