Phthalic acid reacts with resorcinol in the presence of concentrated $H_2SO_4$ to give

Which of the following is the most acidic compound?

$A$ trisubstituted compound '$A$',$C_{10}H_{12}O_2$ gives a neutral $FeCl_3$ test positive. Treatment of compound '$A$' with $NaOH$ and $CH_3Br$ gives $C_{11}H_{14}O_2$,with hydroiodic acid $(HI)$ gives methyl iodide,and with hot conc. $NaOH$ gives a compound $B$,$C_{10}H_{12}O_2$. Compound '$A$' also decolorises alkaline $KMnO_4$. The number of $\pi$ bonds present in the compound '$A$' is $...........$

What is the product of the sulfonation of phenol?

Which one is the most acidic compound?

What is produced when phenol reacts with sodium?