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

The elevation of boiling point of 0.10 m aqueous CrCl₃.xNH₃ solution is two times that of 0.05 m aqueous CaCl₂ solution. The value of x is ______.

[Assume 100% ionisation of the complex and CaCl₂, coordination number of Cr as 6, and that all NH₃ molecules are present inside the coordination sphere]

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)