I thought it was 4.098 as 4 9 and 8 are three sig.figs. but the answer was 4.10, how? 0 is not a sig. fig.
Because the 0 in 4.098 is significant and possess value in the answer.
Say for example the number was 4.09800000, the remaining 0's after the 8 are not relevant and do not affect the number. However 4.098, removing the 0 and changing it to 4.98 does not possess the same value. It's like removing the 0's from 4008 and changing it to 48, it's not the same.
0 is only a significant fig. where it's smooshed between other numbers, if its before or after a number, then it doesn't matter.