One. The zeros are placeholders.
The number of significant digits in an integer ending in zeros is always ambiguous. It is not clear whether the number is accurate to the nearest hundred thousands (1 significant digit), ir to the nearest unit (6 sig digs).
One - the trailing zeros are not significant.
4
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.