Question

How many significant figures does 0.0006510 of have?

Answer 1

It has 4 significant figures. If you see the Zero after the one decimal point you don’t count that and instead just started at 6

Answer 2

There are 4 sig. Fig.s in 0.0006510, the 6510 are significant and the 0.000 are insignificant,  as zeros can not lead and the are not captive zeros, and have no non-zero digit leading them; they are seen as insignificant zeros and not counted.