A radioisotope has a half life of $10$ days. If today there is $125$ $g$ of it left, what was its mass $40$ days earlier?

Q. A radioactive isotope has a half-life of 10 days. If today 125 mg is left over, what was its original weight 40 days earlier

Q. A radioactive isotope has a $t$${}_{1/2}$ of $10$ days. If today there is $125g$ of it left then its weight $40$ days earlier is

Q. A radioactive material has an initial mass of $16g$. After $120$ days it reduces to $0.5g$. Half-life of the radioactive elements is:

Q. Four different radioactive elements are kept in separate containers. In the beginning the container $A$ has $200$ g-atom with half-life of 2 days, $B$ has $20$ g-atom with half-life of $20$ days, $C$ has $2$g-atom with half-life $200$ days and $D$ has $100$ g-atoms with half-life of $10$ days. In the beginning the maximum activity exhibited by the container is: