2Al2O3=4Al+3O2

So,

could be like these ratios?

2mol Al2O3/4mol Al
and
2mol Al2O3/3mol O2
and
etc...

Usually, we write equations that will actually occur, like



So, 4 atoms or moles of aluminum will react with 3 moles of oxygen to produce 2 moles of aluminum oxide.

Now, I'm not sure what "Write all possible mole ratios." means so I don't think I can help you there.

That's why what i was confusing.
it says

following chemical equations write all possible mole ratios.

so..

Don't u have any idea with it?

anyway THanks

I think they mean Al/O = 2/3, 4/6, 6/9, etc.

It might be possible that the formula for aluminum oxide is

.

There are other methods to determine the exact formula of some molecule. In many inorganic materials, the lattice is so extensive, that it's really not possible to say what the true "molecule" is, so they just use the simplest molecular formula.