What are $X$ and $Y$ in the following reaction?

$A$ mixed ether $(P)$, when heated with excess of hot concentrated hydrogen iodide, produces two different alkyl iodides which when treated with aqueous $NaOH$ give compounds $(Q)$ and $(R)$. Both $(Q)$ and $(R)$ give a yellow precipitate with $NaOI$. Identify the mixed ether $(P)$:

When is methyl tert-butyl ether formed?

In which of the following transformations is phosphorus pentachloride $(PCl_5)$ used as a reagent?

Write equations of the following reactions:
$(i)$ Friedel-Crafts reaction - alkylation of anisole.
$(ii)$ Nitration of anisole.
$(iii)$ Bromination of anisole in ethanoic acid medium.
$(iv)$ Friedel-Craft's acetylation of anisole.

Which one of the following,with $HBr$ will give a phenol?