The number of significant figures in 3.500

The number of significant figures in 3.500 is 4.

Here's the step-by-step process:

1. Identify the number: The number given is 3.500.
2. Understand the rules: All non-zero numbers are significant. Any zeros between significant figures are significant. Leading zeros are not significant. Trailing zeros in a number containing a decimal point are significant.
3. Apply the rules: In 3.500, 3 is a non-zero number so it is significant. The zeros after 3 are between significant figures, so they are also significant. The zero at the end is a trailing zero in a number containing a decimal point, so it is significant.
4. Count the significant figures: There are 4 significant figures in 3.500.