The half-life of tritium is approximately 12 years. What will be the molar ratio of tritium to helium-3 in a sealed sampel after 25 years?

Answer 1

k = 0.693/t_1/2
Solve for k and substitute in the equation below.
ln(No/N) = kt
Solve for No/N
Then you want [N/(No-N)]. Check my thinking.