How reactive is Protactinium?

Answer 1

Protactinium react with oxygen, hydrogen, sulfur, halogens, many other elements, mineral acids.
The Pauling electronegativity is 1,5 and is considered a fairly reactive metal.

Answer 2

Protactinium is a highly reactive element, especially in its pure form. It readily reacts with oxygen, water, and most acids. Its reactivity is mainly due to its unstable isotopes, which undergo radioactive decay, releasing energy in the process.