What do you mean by significant figures? State the rules for deciding significant figures

The significant figures in measurement or result are the number of digits known with certainty plus one uncertain digit.

Rules for deciding significant figures:

1. All non-zero digits are significant.
   e.g. 127.34 g contains five significant figures which are 1, 2, 7, 3, and 4.
2. All zeros between two non-zero digits are significant.
   e.g. 120.007 m contains six significant figures.
3. Zeros on the left of the first non-zero digit are not significant. Such a zero indicates the position of the decimal point.
   e.g. 0.025 has two significant figures, 0.005 has one significant figure.
4. Zeros at the end of a number are significant if they are on the right side of the decimal point.
   e.g. 0.400 g has three significant figures and 400 g has one significant figure.
5. In numbers written in scientific notation, all digits are significant.
   e.g. 2.035 × 10² has four significant figures and 3.25 × 10^–5 has three significant figures.