Substance M is a blue, brittle solid. Substance N is a colorless, flammable gas. What can we predict about the compound created when M and N form a covalent bond?

As given

Substance M is a blue, brittle solid: It means it is a solid. However we cannot predict the nature of the element. It can be non metal or metal. So it can be highly electropositive or electronegative. It can lose or gain electron or it may share electrons to form covalent bonds

Similarly

Substance N is a colorless, flammable gas: it must be non metal. But we cannot predict the exact composition or nature of the gas.

Flammable colourless means it can be hydrogen.

So we can say that we cannot comment on the nature of the compound formed by combination of M and N.