An element has two isotopes, $x$ and $Y,$ with mass numbers of $79\mathrm{.}0$ and $82\mathrm{.}0$ respectively. The relative atomic mass is $80\mathrm{.}0.$ The percentage abundance of the two isotopes is

$x-33\%$

$Y-67\%$

$x-25\%$

$Y-75\%$

$x-67\%$

$Y-33\%$

$x-75\%$

$Y-25\%$

$x-50\%$

$Y-50\%$