To express the radius of a hydrogen atom, which is \(0.0000000529177\) millimeters, as an approximation, we can round it to a reasonable number of significant figures.
Looking at the options provided, the closest approximation to \(0.0000000529177\) is:
0.00000005
This is because it rounds down to \(5.3\) when considering two significant figures after the leading zeros, which makes \(0.00000005\) a more appropriate approximation.