It is a physical change because only the states as being changes, not the actual bonds in the compound.
<h3>Answer:</h3>
Oxidation number refers to a number given to an atom which shows the number of number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound.
Hence oxidation number of following atoms in given reaction are:
In NaOH:
Na = +1
O = -2
H = +1
In H2:
H = 0
From my understanding the correct answer would be phyical