Answer
Please see the answer below.
Work Step by Step
In all the given species oxidation number is zero. An element in its elemental state or stable state has zero oxidation number.
$H_{2}$ is the stable state of hydrogen.
$Se_{8}$ is the stable state of Selenium.
$P_{4}$ is the stable state of Phosphorus.
$O$ is the elemental state of Oxygen.
$U$ is the elemental state of Uranium.
$As_{4}$ is the stable state of Arsenic.
$B_{12}$ is the stable state of Boron.
