Explanation

The relative lowering of vapor pressure is given by the formula: 

Relative lowering of vapor pressure = (Mole fraction of solute)/(Mole fraction of solvent + Mole fraction of solute)

Calculating the mole fractions:

Moles of glucose = (18 g / 180 g/mol) = 0.1 mol 

Moles of water = (90 g / 18 g/mol) = 5 mol

Mole fraction of glucose = 0.1 / (0.1 + 5) = 0.02 

Mole fraction of water = 1 - 0.02 = 0.98 

Substituting into the formula:

Relative lowering of vapor pressure = 0.02 / (0.02 + 0.98) = 0.02 / 1 = 0.02 

Therefore, the relative lowering of vapor pressure is 0.02, which is equivalent to 1/50.