Two radioactive samples consist of equal number of atoms.The half lives are 2 hours and 4 hours respectively.The ratio of their activities then is 

let the $N$ no. of atoms in $x$ and $y$ both.

assume $\Delta N$ ho. af atoms decay in \Deltat time.

We knouthe rate of disintegration

$\frac{\Delta N}{Dt}\propto N$

$\frac{\Delta N}{\Delta t}=\lambda N$

we know $\lambda =\frac{0.693}{t/2}$

So ${\lambda }_1=\frac{0.693}{2},{\lambda }_2=\frac{0.693}{4}$

$\frac{y}{x}=\frac{\lambda N}{{\lambda }_{x}N}$

$\frac{y}{x}=\frac{0.693\times 2}{4\times 0.693}$

$\frac{y}{x}=\frac{1}{2}$

$[B]1:2$