In a salt crystal, the distance between adjacent sodium and chloride ions is 2.82 Angstroms (or .282 nm; refer to the supplemental practice document for refreshers on these units). What is the force of attraction between the two singly charged ions?

the grams   of   barium that   are in   2.3 x 10^23   atoms of barium   is   52.4 g (answer c)

    calculation

mass = moles   of ba   x molar   mass of ba

  molar mass of ba from periodic table=   137.3 g/mol

  use the   avogadro's law   constant   to   calculate the moles of barium

  that   is     1 mole =   6.02   x 10^23 atoms

                    ? moles = 2.3 x 10^23   atoms

by cross   multiplication

=(1 mole   x 2.3x 10^23 atoms)   / 6.02   x10^23 atoms)=   0.382   moles

mass   is therefore = 137.3   g/mol x 0.382 mol = 52.4 ( answer c)

explanation:

some sources quote the lethal dose, for an average 170lbs opiate-naive individual is between 75 and 375 mg

there are two significant figures.