How many significant digits does 20.0020 have?

Hint: Significant figures in chemistry are the mathematical values that have certainty and precision while performing mathematical operations in chemistry. Significant figures have certain rules.

Complete step-by-step answer:
Significant figures in chemistry tell us the valuable digits in a particular mathematical operation. Significant figures are calculated through certain rules, which are:
- All the digits that have no zero are significant. For example, 32 have 2 significant figures.
- The zeros that are written before non-zero digits are not significant. For example, 0.0047 have 2 significant figures.
- Zeros that are written between the non- zero digits are significant. For example, 4.009 have 4 significant figures.
- Zeros that are written at the right hand side of the decimal are significant, while if the decimal is not present then the zeros are not significant. For example, 200 have 1 significant figure, while 0.200 have 3 significant figures.
- When any scientific notation is written, it is not significant.
- When the exact number of anything is written, it has an infinite number of significant figures. For example, 20 eggs have infinite significant figures.
We are given a number 20.0020, we have to find its significant figures. Since it has zero before and after the decimals and between the numbers, so all are significant, so, 6 significant figures.
Hence, 20.0020 have 6 significant digits.

Note: For addition or subtraction in significant figures, the values with decimals cannot have more number of digits after the decimal written, as that in the original number. The same applies in division and multiplication of significant figures.