There are three. If not, the final zero should not be present.
4 significant digits.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
5 significant digits.
There are 4 significant digits in 5600.
4
Only 1004.
Five. All nonzero digits are significant and zeros in between significant digits are significant.
It has two significant digits.
3 significant digits.
It has 3 significant digits.
4 significant digits.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
000203 has 3 significant digits.
Three significant digits.