The correct option is A 13.19
Given, [PO3−4]=1 M
pKb(PO3−4)=1.62
PO3−4 in aqueous solution gives OH− ion, hence from ostwald's dilution law
[OH−]=√Kb.C
the relation between POH and Pkb is given by
POH=12[Pkb−logC]
putting the value of Pkb and C we get,
⇒ POH=12[1.62−log1]=0.81
Also,
pH=14−pOH=14−0.81=13.19
Hence, pH of PO3−4 in aqueous solution is 13.19