SOMEONE ANSWER QUICK !! When a sample of blue crystals is heated, a vapour
is given off and a white powder remains. Analyze
whether a physical or a chemical change occurred.
Give reasons for your answer.

there are two pieces of evedence wich piont that this prosses is a chemical change in color and  formation of a new solid whith different color which is why the white powder . therefore the subtance has a new identidty .   sorry but i had to piont out some thing white subtance hmm...COCAINE sorry about that

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:

the answer is true.