# Which statement is correct one and how? 1- Which number has three significant figures? 2- Which number has three significant digits?

Either statement is correct, because they mean the same thing. For example, $\text{0.0505 g}$ has three significant figures if three digits are needed to fully describe the uncertainty you have in your measurement.
The three significant digits, or significant figures, are "$\text{505}$". Read this question for more background on significant figures if you don't see why.
In a greater context, consider measuring with a mass balance that has an uncertainty of $200$ $\mu g$ (typical at my undergraduate university), or $\text{0.0002 g}$.
This means that if the above mass was measured on this balance, then you would report your measurement as $0.0505$ $\left(\pm 0.0002\right)$ $\text{g}$, and your acceptable range for comparing to a literature value would be $0.0503 - 0.0507$ $\text{g}$. A literature value outside this range would be considered statistically different.