Answer is: the number of bromine molecules is 1.35·10²⁴.
n(Br₂) = 2.25 mol; amount of bromine molecules.
Na = 6.022·10²³ mol⁻¹; Avogadro constant.
N(Br₂) = n(Br₂) · Na.
N(Br₂) = 2.25 mol · 6.022·10²³ mol⁻¹.
N(Br₂) = 13.54 ·10²³.
N(Br₂) = 1.35·10²⁴; number of bromine molecules.
