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

$A$ radioactive sample is emitting $64$ times more radiation than the non-hazardous limit. If its half-life is $2 \ hr$,after what time will it become non-hazardous? $(hr)$

$A$ wood specimen from an archeological site shows a $_6^{14}C$ activity of $5.0 \ counts/min/gm$ of carbon. If a freshly cut wood gives $15 \ counts/min/gm$ of carbon,what is the age of the specimen? (Given: $t_{1/2}$ for $_6^{14}C$ is $5000 \ years$)

The half-life of radioactive $C^{14}$ is $5760 \ years$. In how many years will a $200 \ mg$ sample of $C^{14}$ be reduced to $25 \ mg$?

The half-life of $_6C^{14}$ if its decay constant $k$ or $\lambda$ is $2.31 \times 10^{-4} \ yr^{-1}$ is:

Radium has an atomic weight of $226$ and a half-life of $1600$ years. The number of disintegrations produced per second from $1 \ g$ of radium is: