Answer:
Option C
Explanation:
The reaction of white phosphorus with aqueous alkali is
$P_{4}+3NaOH+3H_{2}O \rightarrow PH_{3}+NaH_{2}PO_{2}$
In the above reaction phosphorus is simultaneously oxidized
$[P_{4}(O) \rightarrow NaH_{2} P^{+1}O_{2}]$ as well as reduced [$P_{4}(0) \rightarrow PH_{3}]$
Therefore, this is an example of disproportionation reaction. Oxidation number of phosphorus in $PH_{3}$ is -3 and in $NaH_{2}PO_{2}$ is +1.
However,+1 oxidation no. is not given in any option, one might think that $NaH_{2}PO_{2}$, has gone to further decomposition on heating.
$2NaH_{2}PO_{2}$ $\underrightarrow{\triangle} Na_{2}H^{+5}PO_{4}+PH_{3}$
