Two perfumes are released at the same time. if one is standing 7.5 m from the point of release. perfume a (molar mass 275 g/mol) and perfume b (molar mass 205 g/mol) at the same temperature. i. which perfume will the person smell first and why?

According to Graham's Law of Diffusion," Diffusion of Gas is inversely proportional to square root of its Molecular Mass or Density".

                          rᵇ/rᵃ  =  
Or,
                          rᵇ/rᵃ  =       ----- (1)
As, 
                          Ma  =  275 g/mol

                          Mb  =  205 g/mol

Putting Values in eq.1,

                          rᵇ/rᵃ  =  

                          rᵇ/rᵃ  =  1.15

Result:
          Perfume B will diffuse 1.15 times faster than Perfume A. Hence, Perfume B will be first smelled by the person.