The major product of the following reaction sequence is

In the following sequence of reactions,a compound $A$ (molecular formula $C_{6}H_{12}O_{2}$) with a straight chain structure gives a $C_{4}$ carboxylic acid. $A$ is :
$A$ $\xrightarrow{LiAlH_{4} / H_{3}O^{+}} B$ $\xrightarrow{\text{Oxidation}} C_{4} \text{ carboxylic acid}$

Draw the structures of the following compounds:
$(i)$ $3-$Methylbutanal
$(ii)$ $p-$Nitropropiophenone
$(iii)$ $p-$Methylbenzaldehyde
$(iv)$ $4-$Methylpent$-3-$en$-2-$one
$(v)$ $4-$Chloropentan$-2-$one
$(vi)$ $3-$Bromo$-4-$phenylpentanoic acid
$(vii)$ $p, p^{\prime}-$Dihydroxybenzophenone
$(viii)$ Hex$-2-$en$-4-$ynoic acid

Ethanoic acid $+$ $3$-methylbutan-$1$-ol $\underset{\text{traces } H_2SO_4}{\longleftrightarrow} (A)$; Compound $(A)$ is

Which of the following has highly acidic hydrogen?

In the reaction sequence,$[X]$ is a ketone:
$[X] \xrightarrow{KMnO_4/OH^{-}/\Delta} HOOC-(CH_2)_3-CH(CH_3)-COOH$
$[X]$ will be: