If we know the half life how could we determine what percentage of radioactive isotopes will be left after 4 half-lives?

"After 1 half-life there will be 50% of the original isotope, and 50% of the decay product.

After 2 half-lives there will be 25% of the original isotope, and 75% of the decay product.

After 3 half-lives there will be 12.5% of the original isotope, and 87.5% of the decay product.

After 4 half-lives there will be 6.25% of the original isotope, and 93.75% of the decay product." -Stephen Frantz, Former Director of the Reed College Nuclear Reactor

Explanation:

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance