How reactive is Holmium the element?
Actually, holmium is very reactive. It will react with just about anything including water and o2... Which is why it is so rare. As to your question you can say its very reactive (not as much as F)
It varies among what other elements there are to react with.
Holmium is too reactive to be got uncombined in nature. When separate, it is moderately stable in dry air at room temperature. However, it is known to reacts with water and rusts very easily, and it does also burn in air when heated.