Context: Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known, but only one binary aluminium hydride. Binary indium hydride has not yet been identified, although larger complexes exist.

Question: How many binary borane hydrides are known?
Answer: over 100

Question: How many binary aluminum hydrides are there?
Answer: 1