It is difficult to say with integers ending in zero. The number could be acurate to the units' place or to the millionths' place (or anything in between). Therefore, there could be 1 to 7 sf.
4
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 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.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
000203 has 3 significant digits.
Three significant digits.