I think it's fairly common knowledge that matter and antimatter annihilate each other on contact. But what happens if two dissimilar atoms collide?
For example, what happens if a Hydrogen atom (1 proton, 1 electron) contacts an antihelium atom (2 antiprotons, 1 antineutrons, 2 positrons)? Are we left with a new antideuterium atom? Do all the remaining particles fly apart? Does something even more exotic happen?