Which measurement is the largest?

The largest measurement among the options is 1.0 g because it is equal to 1000 mg, which is significantly more than any of the other listed amounts.

When comparing the other measurements, 0.1 g is equal to 100 mg, which is much smaller than 1.0 g. The measurement of 500 mg is also less than 1.0 g, as it is only half a gram. Finally, 0.25 g is equal to 250 mg, which again is still smaller than 1.0 g. Thus, 1.0 g stands out as the largest measurement in this comparison.