Question

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.

Answer 1

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)

Answer 2

N= number of molecules
n= 2.3x10^23/6.022x10^23
  = 0.381 mol

Now,
M= molar mass in g/mol
m= mass in grams
m=nxM
   =0.381 molx137 g/mol
   = 52.197g

So, the correct answer should be C