To find the slope of the arithmetic sequence, we need to determine the common difference between the number of muffins baked on consecutive days.
- From day one to day two: 11 muffins - 5 muffins = 6 muffins
- From day two to day three: 17 muffins - 11 muffins = 6 muffins
The common difference (or slope) is 6.
Therefore, the correct answer is:
6