There would be five significant figures because of the lack of a decimal or a bar over the final zero indicating that it (not the 9) was the final, estimated (but still measured, and therefore still significant) digit.
Finding the right significant figures can be a bit confusing for some people. As long as you know how to find the right significant figures, this will not be too complicated.
You can simply know the rules of significant figures to make it easier. The first rule to follow is that all non-zero digits are significant. The second rule is the zeroes that are in between two non-zero digits are also significant.
A final zero in the decimal portion of the number will also be considered as significant. Based on these rules, you can say that the significant figures in the above-mentioned number are five (5).
All non-zero digits are significant.
Zeros between digits are significant.
Zeros at END of a COUNTED quantity are NOT significant.
Zeros in front of a number are not significant.