Consider the following reactions
'A' is :

The set that contains atomic numbers of only transition elements, is :

In an estimation of bromine by Carius method, 1.6 g of an organic compound gave 1.88 g of AgBr. The mass percentage of bromine in the compound is _______.
(Atomic mass, Ag = 108, Br = 80 g mol^–1)

The number of Cl = O bonds in perchloric acid is, "________".