To find the percentage error, use the following formula:

\[
\text{Percentage Error} = \frac{\text{Absolute Error}}{\text{Actual Value}} \times 100\%
\]

Here:
- The measured length is \(8.5\) cm.
- The actual length is \(8.6\) cm.
- The absolute error is \(|8.5 - 8.6| = 0.1\) cm.

Plug these values into the formula:

\[
\text{Percentage Error} = \frac{0.1}{8.6} \times 100\%
\]

Calculate the percentage:

\[
\text{Percentage Error} = \frac{0.1}{8.6} \times 100 \approx 1.16\%
\]

Thus, the percentage error is:

B. 1.16%