Carbolic acid is oxidised by acidified sodium dichromate to give

When phenol is treated with $PCl_5$,the yield of chlorobenzene is generally poor because of the formation of

The main product of the following reaction will be:

The reaction is given as: $X \xrightarrow{Y} \text{Benzoquinone}$. Identify $X$ and $Y$ in the above reaction.

When phenol is reacted with $CHCl_3$ and $NaOH$ followed by acidification,salicylaldehyde is obtained. Which of the following species are involved in the above mentioned reaction as intermediates?

Which of the following is most acidic?