How many significant figures are in 2.010?

Answer 1

When to the left of the decimal point, zeros mean nothing: 2010 has 3 sig figs (counting 201 as individual numbers 2, 0, and 1 which equals 3). When to the right, they do mean something: 0.0045 has 4 sig figs (counting 0045 as individual numbers 0, 0, 4, and 5 which equals 4).

Answer 2

Assuming the final zero is not there simply to use up ink, there are 4.