Determine the number of significant digits in the value 100.10 .

According to the rules for determining significant figures, all non-zero digits are significant. Zeros between non-zero digits are significant, and trailing zeros in a number containing a decimal point are also significant.

In the given value $100.10$, the non-zero digits $1$ are significant. The zeros between the non-zero digits are significant. The trailing zero after the decimal point is also significant.

Therefore, all five digits in $100.10$ are significant. The number of significant digits is $5$.