why is it that when water is decomposed through a process call electrosys (when electricity is put through water)there is more volume of hydrogen than oxygen produced?

Answer 1

Because water molecules contain twice as many H atoms as O atoms. Both hydrogem and oxygen atoms form molecules in pairs, so you also have twice as many H2 molecules as O2 molecules.

The volume of a gas is proportional to the number of molecules in it, and does not depend upon the mass of the molecule. So there is also twice the volume of hydrogen, compared to oxygen.