If the amount of radioactive substance is increased three times,the number of atoms disintegrated per unit time would

The half-life of the radio element $_{83}Bi^{210}$ is $5 \ days$. Starting with $20 \ g$ of this isotope,the amount remaining after $15 \ days$ is ......... $g$. (in $g$)

$A$ freshly prepared radioactive source of half-life $2 \ hours$ emits radiations of intensity which is $64$ times the permissible safe level. The minimum time after which it would be possible to work safely with this source is ......... $hours$.

If $3/4$ of a radioactive element disintegrates in $2$ hours,its half-life would be

The half-life period of a radioactive metal is $20 \ days$. What fraction of the metal remains after $80 \ days$?

$A$ radioactive element gets spilled over the floor of a room. Its half-life period is $30$ days. If the initial activity is ten times the permissible value,after how many days will it be safe to enter the room?