JEE Main · 2010 · 11 Apr 2010 · Offline · Units & Measurement

In $23.023$ every digit counts, the non-zero digits and the zero trapped between them, giving five significant figures. In $0.0003$ the leading zeros only fix the decimal place and are not significant, so only the $3$ counts, one significant figure. In $2.1\times 10^{-3}$ the power of ten is merely a scale factor and both digits of the coefficient $2.1$ are significant, giving two. The counts are $5,1,2$.