Identify the correct statements with reference to the given reaction
P4 + 3OH- + 3H2O → PH3 + 3H2 PO-2
The above reaction shows that P4 undergoes reduction and oxidation simultaneously showing an example of disproportionation reaction. The oxidation number in P4 is zero as there are all elemental toms of phosphorous bonded in a pyramidal geometry. The oxidation reaction in results in the formation of Hypophosphite ion H2PO-2, which has an oxidation state of 
Thus showing oxidation of P atom from 0 to +1. In case of phosphine the hydrogen involves has +1 ON number thus P having ON of -3, showing P is undergoing reduction.
In option (iv) it is stated that hydrogen is neither oxidant nor reductant but for H2O, H2 being in +1 state throughout the entire reaction it neither undergoes oxidation nor reduction, thus Option (iv) is correct.