All atoms of a particular element have a unique no. of protons. The number of significant figures for a number tells us the precision of that number. Nonzero digits are always significant. Leading zeros precede all of the nonzero digits. They are not significant.
Captive zeros are between nonzero digits.
They are always significant. Trailing zeros follow the nonzero digits. They are significant if the number contains a decimal point. Exact numbers have an infinite number of sig. The number of sig.