The respective number of significant figures for the numbers  $23.023, 0.0003$and  $2.1\times {10}^{-3}$are

In   $2.1\times {10}^{-3}$number of significant figures will be  because all the zero’s between non zero digits are significant. In  ,$0. 0003$ number of significant figures will be one because all the zero’s before and after decimal point are insignificant if the number is less then one. In  $2.1\times {10}^{-3}$number of significant figure are to because power of 10 is not considered as significant  figure