What is the mass of an original 5.60 gram sample of iron 53 that remains on uncharge after 25.53 minutes?

Answer is: 0,7g.

m (Fe) = 5,60g.

t1/2 (Fe-53) = 8,51 min.

t1/2 - half-life of iron.

25.53 min/8.51 min = 3 half lives.

one half-life - mass of iron is reduced by half.

first half life - 5,60g → 2,80g.

second half life - 2,80g → 1,40g.

third half-life - 1,40g → 0,7g.