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

The correct option is 5, 1, 2.

To find the number of significant figures for each of the given numbers, we apply the standard rules of significant figures step-by-step:

1. For the number 23.023:
- All non-zero digits are significant (2, 3, 2, and 3).
- Any zeros between non-zero digits are also significant (the zero between 3 and 2).
- Therefore, all 5 digits (2, 3, 0, 2, 3) are significant.
- Number of significant figures = 5.

2. For the number 0.0003:
- Leading zeros (zeros to the left of the first non-zero digit) serve only as placeholders to locate the decimal point and are not significant.
- Only the non-zero digit 3 is significant.
- Number of significant figures = 1.

3. For the number $2.1\times {10}^{-3}$:
- In scientific notation, the numerical portion (the mantissa) determines the number of significant figures, while the power of 10 is not counted.
- For the part 2.1, both digits (2 and 1) are non-zero and therefore significant.
- Number of significant figures = 2.

Combining these results, the respective number of significant figures for the numbers 23.023, 0.0003, and $2.1\times {10}^{-3}$ are 5, 1, and 2.