Decay of $_{92}U^{235}$ is $...$ order reaction.

The half-life period of a radioactive substance is $8 \ years$. After $16 \ years$,the mass of the substance will reduce from starting $16.0 \ g$ to ....... $g$.

The half-life of $_{92}U^{238}$ is $4.5 \times 10^9$ years. After how many years,the amount of $_{92}U^{238}$ will be reduced to half of its present amount?

The half-life of a radioactive isotope is $3 \ hours$. If the initial mass of the isotope is $256 \ g$,how much mass in $g$ will remain after $18 \ hours$ (in $.0$)?

The $C^{14}$ to $C^{12}$ ratio in a wooden article is $13\%$ that of the fresh wood. Calculate the age of the wooden article. Given that the half-life of $C^{14}$ is $5770 \ years$.

If the half-life of a certain radioactive nucleus is $1000 \ s,$ the disintegration constant is