The number of Pbr3 that contain 3.68 x10^ 25 bromine atoms is 60.631 moles
calculation
by use of Avogadro law constant
that is, 1 moles = 6.02 x10^23 atoms
what about 3.65 x10^25 atoms
by cross multiplication
= (1 mole x 3.65 x 10 ^25 atoms) / ( 6.02 x10^23 atoms) = 60.631 moles
atoms and atoms cancel out each other
His the answer I hope it helps
In chemistry the need for standards when measuring quantities are in place for accurate measurement that is recognized world wide. This way, no matter what language people use, they will always understand there standards.