Molality is defined as the number of moles of solute per kilogram of solvent (not solution). It is temperature-independent and preferred for colligative property calculations. Moles of glucose (= 18/180 = 0.1) mol. Mass of solvent (water) (= 500) g (= 0.5) kg. Molality (m = 0.1/0.5 = 0.2) mol/kg (= 0.2) m. Option 0.1 m would result if the solvent were taken as 1 kg (1000 g), but here only 500 g is used. Option 0.5 m would result from incorrectly using 0.2 mol of glucose instead of 0.1 mol. Option 1.0 m would require either 0.1 mol in 100 g of water, or 0.5 mol in 500 g — neither matches. This question applies the NCERT definition of molality, distinguishing it from molarity which uses solution volume. Plausibility check: molality is expressed in mol/kg; (0.1 , \text{mol} \div 0.5 , \text{kg} = 0.2 , \text{m}), with consistent units throughout.