A substance is on its fifth half-life. Which approximates the percentages of radioactive and stable isotopes, respectively? 96.9%; 3.1% 3.1%; 96.9% 12.5%; 87.5% 87.5%; 12.5%

The answer is 3.1%; 96.9%. The formula to find the remaining radioactive material is (1/2)ⁿᵘᵐᵇᵉʳ ᵒᶠ ʰᵃˡᶠ⁻ˡᶦᵛᵉˢ, meaning (1/2)⁵ is 0.031. Converting this to a percentage, 3.1% is the remaining radioactive material while 96.9% is the percentage of the stable isotopes.