$\mathrm{A}+{\mathrm{B}}_{\left(\mathrm{steam} \mathrm{volatile}....\right)}\stackrel{\mathrm{dil}.{\mathrm{HNO}}_3}{\leftarrow }\mathrm{phenol}\stackrel{\mathrm{Conc}.{\mathrm{HNO}}_3}{\to }\mathrm{C};$  correct oder of P^ka values is 

-NO₂ group increases the acidic strength of phenol

 acidic strength of    

This is because in o-nitrophenol, chelation occurs due to intra molecular H-bonding.

Proton is less available for donation.

$\therefore$Acidic strength of p-nitro phenol>o-nitro phenol>phenol.

P^ka of B>A>C