How long does it take for 87.5 % of each isotope(Krypton-73, Krypton-74, Krypton-76, and Krypton-81) to decay?

1st half-life: 100%/2 = 50%
2nd half-life: 50%/2 = 25% + 50% (from first half-life)
3rd half-life: 25%/2 = 12.5% + 75% (from first and second half-lives

I looked it up...

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later

If you open the bottle of perfume then nothing but the smell will come out of it and yes it is a type of gas smell because it’s say it in english so i can understand better and you