Which of the following is a valid IPV$4$ subnet mask?

BA$98$:$1234/64$

$255\mathrm{.}255\mathrm{.}255\mathrm{.}255$

$0\mathrm{.}0\mathrm{.}255\mathrm{.}255$

$255\mathrm{.}255\mathrm{.}240\mathrm{.}0$