The measurement <em>1246g</em> shows four figures. To show this measurement to <em>three signficant figures</em> you must change the last digit to 0 and round properly.
To report the measurement 1246g to three significant figures you must replace the last digit (the 6) with 0 and round the previous one (the 4) to the closest integer: 1250 is closest to 1246 than 1240, so the correct rounding is 1250.
In an integer number, the zeros after the last none zero digit are not sginificant figures; that is why the zero in 1250 g is not significant and this number has just three significant figures.
I would imagine that n-butanol would have the higher boiling point because it has less branching and therefore stronger intermolecular forces between molecules.
