Number of Br atoms : 2.679 x 10²³
Further explanation
The mole is the number of particles contained in a substance
1 mol = 6.02.10²³
Moles can also be determined from the amount of substance mass and its molar mass
[tex]\tt mol=\dfrac{mass}{MW}[/tex]
Proust stated the Comparative Law that compounds are formed from elements with the same Mass Comparison so that the compound has a fixed composition of elements
[tex]\tt mass~Br=\dfrac{2.Ar~Br}{MW~CH_2Br_2}\times mass~CH_2Br_2\\\\mass~Br=\dfrac{2.80}{174}\times 38.7=35.59~g[/tex]
[tex]\tt \dfrac{35.59}{80}=0.445[/tex]
[tex]\tt 0.445\times 6.02\times 10^{23}=\boxed{\bold{2.679\times 10^{23}}}[/tex]
