Molar mass of Glucose, C6H12O6 = 180 g mol-1
Mass % can be calculated as
= ( Mass of element / Molar mass)100
Mass % of Carbon = [(612) / (180)]100
= 40
Mass % of Oxygen = [(616) / (180)]100
= 53.33
Mass % of hydrogen = [(121) / 180]100
= 6.67