\[-COOH\xrightarrow[{{H}_{2}}O]{LiAl{{H}_{4}}}-C{{H}_{2}}OH\]       \[\xrightarrow{PB{{r}_{3}}}-C{{H}_{2}}Br\xrightarrow[DMSO]{KCN}\]      \[-C{{H}_{2}}CN\xrightarrow[{{H}_{2}}O]{{{H}^{+}}}-C{{H}_{2}}COOH\]

DIBAL-H is a bulkier reducing agent. It reduces both ester and carboxylic group into an aldehyde ( partial reduction ) at low temperature.

$$p{K_a} = - \log \,{K_a};\,HCOOH$$      is the strongest acid and hence it has the highest $${K_a}$$  or lowest $$p{K_a}$$  value.

Selenium dioxide oxidises aldehydes and ketones at \[\alpha \] - position to carbonyl group. \[C{{H}_{3}}CHO\xrightarrow{Se{{O}_{2}}}OHC.CHO\]

Weaker the base, better the leaving group and hence more is the reactivity of the compound. The relative basic character of the four groups is \[NH_{2}^{-}>O{{R}^{-}}>OCOCH_{3}^{-}>C{{l}^{-}}\]
Thus the relative leaving ability of the four groups is $$NH_2^ - < O{R^ - } < OCOCH_3^ - < C{l^ - }$$
Hence the relative reactivity of the four acyl derivatives toward nucleophile is

Alkaline $$KMn{O_4}$$  converts complete carbon chain ( that is directly attached to benzene nucleus ) to $$-COOH$$   group. $$B{r_2}$$  in the presence of halogen carrier causes bromination by electrophilic substitution reaction and ethyl alcohol in acidic medium results in esterification.

$$\eqalign{ & {\text{Here}}\,\,x = NaOH + CaO\,{\text{(soda line)}} \cr & y = Zn\,\,{\text{dust}} \cr} $$

It is an example of intramolecular cannizzaro reaction.