Significant figures are the digits which play a role in defining a measurement that is they carry some meaning.
There are three essential rules to find out the significant figures in a given number:
Rule 1: Non-zero digits such are always significant.
Rule 2: The zeroes after a non-zero number in decimal are also significant. An example is if the number is 0.0500 then the zeroes after 5 are considered significant, however, the zeroes before 5 are not significant.
Rule 3: The zeroes placed between any two significant digits are also considered as significant e.g in 202 the zero is significant.
Therefore, in the number 0.020 km, there are two significant digits, one is 2 and the other is the last zero placed after 2.
