Question $5$ assist with $5\mathrm{.}15\mathrm{.}2$ and $5\mathrm{.}3$

$[18]$

$5\mathrm{.}1)$ Propose a mechanism for the acid$-$catalyzed reaction shown below:

$(8)$

$5\mathrm{.}2)$ Arrange the following carbonyl compounds in order of incroasing $(<mtext\; id="EditorElement\_34258"></mtext><mi\; id="EditorElement\_34259">)</mi>$ reactivity toward nucleophilic addition.

$(4)$

$5\mathrm{.}3)$ Propose a mechanism for the following reaction:

$(6)$