Answer:-
3.77 x 10²¹ arsenic(iii) oxide molecules correspond to an LD50 value of 0.0146 for a 187 lb man
Explanation: -
Weight of man = 187 lb
             = [tex]\frac{187 lb}{2.2 lb} x 1 kg[/tex]
             = 84.8 Kg
LD50 = number of grams of a substance that is lethal to 50% of animals per kilogram of body weight
0.0146 = [tex]\frac{number of grams }{Weight of man in kg}[/tex]
Thus
Number of grams of lethal substance = 0.0146 x 84.8
                                = 1.24 g
Molar mass of arsenic(iii) oxide = 197.841 g/mol
Number of moles of arsenic(iii) oxide = [tex]\frac{Mass}{Molar mass}[/tex]
                               = [tex]\frac{1.24}{197.841}[/tex]
                               = 0.00627 moles
Number of molecules of arsenic(iii) oxide = Number of moles x Avogadro number
                                = 0.00627 x 6.02 x 10²³
                                = 3.77 x 10²¹
