Three, four or five. Integers ending in 0 are ambiguous cases.
3 of them.
40500 mg
There are 3 significant figures in this measurement.
2
3
3 of them.
Three of them
40500 mg
2 significant figures.
There are 2 significant figures in this measurement.
There are 3 significant figures in this measurement.
There are 3 significant figures in this measurement.
2
3
4
3 of them.
52.8005 mg to five significant figures is 52.801 mg.