what is the smoke being produced when magnesium is burned (exposed to oxygen) in a crucible?

Question

is the smoke relevant to the ratio of magnesium to oxygen (Mg:O) in the chemical equation, 2Mg + O2 = 2MgO?

There is still a solid within the crucible, which I believe is the MgO, so if the solid is the MgO, is the smoke also MgO? Also, would the Mg:O ratio be affected if the smoke had escaped and the crucible was not covered (to prevent it's escape throughout the experiment)?

The smoke is pretty much coming from the Mg being burned and/or the burnt MgO

Answer 1

When Mg burns in air (O2 and N2) both MgO and Mg3N2 are formed.

Answer 2

There is only one product (you have written down the relevant equation), so that is what the smoke must be, assuming (and you would be right to assume) that it is not coming from anything in the crucible.