Niobium-91 has a half-life of 680 years. after 2,040 years, how much niobium-91 will remain from a 300.0-g sample?
3 g
18.75 g
37.5 g
100.0 g

37.5 g

Explanation:

Radioactive decay follows first order kinetics.

Thus Half-life of sample of Niobium-91 = 680 years

N= amount left after time t

= initial amount

t= time of decay

= 300 g, t= 2040 years,

N=37.5g

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:

c.

explanation: