2) E

We need to use the formula: n=m/Mr to find out the moles of each of the elements in the compound.
mass of iodine = 63.6g
Mr of Iodine = 127
moles = 63.5 ÷ 127 = 0.5 moles

mass of oxygen = 20g
Mr of oxygen = 16
moles of oxygen = 20 ÷ 16 = 1.25

Molar ratio = 1.25 ÷ 0.5 = 2.5
So for ever 1 mole of iodine, there will be 2.5 moles of oxygen. This can only be seen in option E.

I₂O₅. Molar ratio = 5 ÷ 2 = 2.5

So E is correct.