If a sample of barium contains 2.3 x 1023 atoms of barium, how many grams of barium are in the sample? a) 0.38 g. b) 2.62 g. c) 52.4 g. d) 359.5 g.

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

 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)

it means there are 3 atoms of oxygen