Read this: In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranes.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What group is briging ligands most common in?
group 13