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

1. $23.023$: All digits are non-zero or trapped zeros. Total $=5$.2. $0.0003$: Leading zeros are not significant. Only '3' is. Total $=1$.3. $2.1\times 10^{-3}$: Scientific notation '2.1' has two significant figures. Total $=2$.