* General Rules:

* The oxidation number of hydrogen is usually +1, except when it's bonded to metals, in which case it's -1.

* The sum of the oxidation numbers in a neutral compound is zero.

* Applying the Rules:

* We know that the oxidation number of hydrogen is typically +1.

* Arsenic (As) is a metalloid, and we don't have a clear indication that it's acting as a metal in this compound.

* There are three hydrogen atoms, so their total oxidation number contribution is +3.

* To balance this, the arsenic must have an oxidation number of -3.

Therefore, the oxidation number of H in AsH₃ is +1.