Many students are perplexed by the significant figures rules for zeros. Most accept that non-zeros are significant but become uncertain (pun intended) when considering zeros. It is easiest to consider the zeros from the left to the right of non-zeros.
Zeros to the left of non zeros are always insignificant.
Zeros placed between non zeros are always significant.
These zeros are a little more tricky. The presence of a decimal makes the difference. If a decimal is present then zeros to the right of the non zeros are significant. If a decimal is absent then the zeros to the right of the non zeros are insignificant.