Initial mass of a radioactive element is $40 \ g$. How many grams of it would be left after $24 \ years$,if its half-life period is $8 \ years$?

The decay constant of a radioactive sample is $\lambda$. The half-life and mean life of the sample are respectively

$^{226}Ra$ disintegrates at such a rate that after $3160 \ years$ only one-fourth of its original amount remains. The half-life of $^{226}Ra$ will be .......... $years$.

$A$ radioactive isotope decays at such a rate that after $192 \ min$ only $1/16$ of the original amount remains. The half-life of the radioactive isotope is ....... $\min$

$A$ radioactive element has a half-life of $200 \ days$. The percentage of original activity remaining after $83 \ days$ is $....$ (Nearest integer).
(Given: $\text{antilog } 0.125 = 1.333$,$\text{antilog } 0.693 = 4.93$)

The decay of $_{92}U^{235}$ is a reaction of .......... order.