1. Calculate the moles of glucose:

* Molar mass of glucose (C6H12O6):

(6 * 12.01 g/mol) + (12 * 1.01 g/mol) + (6 * 16.00 g/mol) = 180.18 g/mol

* Moles of glucose:

90 g / 180.18 g/mol = 0.5 mol

2. Calculate the mass of water in kilograms:

* Mass of water: 800 g

* Mass of water in kilograms: 800 g / 1000 g/kg = 0.8 kg

3. Calculate the molality:

* Molality (m): Moles of solute / kilograms of solvent

* Molality: 0.5 mol / 0.8 kg = 0.625 mol/kg

Therefore, the molality of the glucose solution is 0.625 mol/kg.