How many significant figures are in the measurement 0.0034 kg?
For starters, you should know that non-zero digits are always significant.
So right from the start, you know that this measurement has at least two significant figures,
#0.0034 ->#two non-zero digits #=#two sig figs
Now, are the zeroes significant as well?
The answer is no. The reason is that zeroes that come after the decimal point are only significant if the number is greater than
#color(red)(color(black)(1.)00color(black)(34)# #->#the zeroes are significant because they follow the decimal point for a number that is #>1#
#0.1color(red)(00)34 ->#the zeroes are significant because they are sandwiched between two non-zero digits for a number that is #<1#
In your case, you have a number that is smaller than
Therefore, your measurement will have