1. Rule for significant figures

   • All non-zero digits are significant.
   • Zeros between non-zero digits are significant.
   • Leading zeros are not significant.
   • In scientific notation, only the digits in the coefficient count as significant figures.

2. For $23.023$

   • Digits are: $2,3,0,2,3$
   • The zero is between non-zero digits, so it is significant.
   • Hence, number of significant figures $= 5$.

3. For $0.0003$

   • All the zeros before $3$ are leading zeros.
   • Leading zeros are not significant.
   • Only digit $3$ is significant.
   • Hence, number of significant figures $= 1$.

4. For $2.1 \times 10^{-3}$

   • In scientific notation, significant figures are counted only in the coefficient $2.1$.
   • The coefficient $2.1$ has two significant digits: $2$ and $1$.
   • Hence, number of significant figures $= 2$.

5. Final tuple $(5,\;1,\;2)$

6. Compare with options

   • Option A: $5,1,2$ ✅
   • Option B: $5,1,5$ ❌
   • Option C: $5,5,2$ ❌
   • Option D: $4,4,2$ ❌

Therefore, the correct option is A.