The empirical formula Of Tin oxide is calculated as follows
Find the mass of oxygen = 0.635 - 0.500 = 0.135
then calculate moles of each element
moles =mass/molar mass
that is Tin(Sn) = 0.500/118.71 = 4.21 x10^-3 moles
for oxygen= 0.135/16= 8.44 x10 ^-3 moles
find the mole ratio by dividing with the smallest mole (4.21 x10^-3)
Sn = ( 4 .21 x10^-3) / (4.21 x10^-3)= 1 mole
O= (8.44 x10^-3 ) /(4.21 x10^-3) = 2 mole
therefore the empirical formula = SnO2