Question

Round off 0.043 to one significant figure

Answer 1

Hey there :)

0.043
The first 0 before the decimal point is not significant since it is used for cosmetic purpose
The 0 after the decimal is not significant as the 0 is used to locate the decimal point
The 4 is the first nonzero integer and it counts as a significant figure

Therefore, 0.04 will be your answer rounded to 1 s.f

Answer 2

In this case the first figure that is significant is 4, 
when we look after 4, we see 3 , so we do not have increases 4, we are going to leave it
0.043≈0.04 (your answer)

if after 4 you would see 5, 6, 7, 8,or 9
you would increase 4 by one, for example 0.047≈0.05