What is the order of radioactive decay of a substance?

The half-life of $10 \ g$ of a radioactive substance is $10 \ days$. The half-life of $20 \ g$ of the same substance is .......... $days$.

If the half-life of a substance is $5 \, \text{years}$,then the total amount of substance left after $15 \, \text{years}$,when the initial amount is $64 \, \text{grams}$,is ....... $\text{gm}$.

What is the half-life period of tritium (in $years$)?

$8 \ g$ of a radioactive substance is reduced to $0.5 \ g$ after $1 \ hour$. The ${t_{1/2}}$ of the radioactive substance is ......... $\min$.

The disintegration constant for a radioactive substance is $0.58 \, hr^{-1}$. Its half-life period is $........ \, hr$.