Is rubbing alcohol with seventy percent alcohol a substance or a mixture?

Chemically speaking alcohol is meant to be ethanol, which is a pure compound with formula CH3CH2OH, it definitely is not a mixture, except when 'dissolved' in water (most stable solution: 4% water + 96% ethanol. (This is what you get when buying a bottle pure ethanol)
rubbing alcohol is a mixture

If you were to take 'alcohol' into a more specific definition an alcohol is really a hydrocarbon with the functional group

So if it were, well i would say, 100% ethanol then it would be a compound.