Radioactive substances do not emit

A sample contains $16\, gm$ of a radioactive material, the half life of which is two days. After $32\, days,$ the amount of radioactive material left in the sample is

Consider a radioactive nucleus $A$ which decays to a stable nucleus $C$ through the following sequence : $A \to B \to C$ Here $B$ is an intermediate nuclei which is also radioactive. Considering that there are $N_0$, atoms of $A$ initially, plot the graph showing the variation of number of atoms of $A$ and $B$ versus time. 

$16\, gm$ sample of a radioactive element is taken from Bombay to Delhi in $2\, hour$ and it was found that $1\, gm$ of the element remained (undisintegrated). Half life of the element is

The half-life of a sample of a radioactive substance is $1$ hour. If $8 \times {10^{10}}$ atoms are present at $t = 0$, then the number of atoms decayed in the duration $t = 2$ hour to $t = 4$ hour will be

If the half life of a radioactive sample is $10\, hours$, its mean life is ..........$hours$