The respective number of significant figures for the numbers 23.023, 0.0003 and 2.1×10-3 are

The reliable digit plus the first uncertain digit is known as significant figures.For the number 23.023, all the non-zero significant, hence 5.For the number 0.0003, number is less than 1, the zero(s) on the right of decimal point but to the left of the first non-zero digit are not significant, hence 1.For the number 21×10-3, significant figures are 2.