(a) (i) Since,As we know that, acid reacts with base to give salt and water Compound $A$ will be acidic in nature with carboxylic acid group.Chemical equation for acid and base reaction:$\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$$\mathrm{HX} + \mathrm{MOH} \rightarrow \mathrm{MX} + \mathrm{HOH}$ Thus, Compound 'A is $\mathrm{CH}_3\mathrm{COOH}$ it is acidic in nature containing a carboxyl functional group.(ii) Carboxylic acids can react with alcohols to form esters in a process called Fischer esterification. An acid catalyst is required and the alcohol is also used as the reaction solvent.(1) Compound B is Ethanol and C is Ethyl acetate.(2) $\mathrm{HCl}$ act as catalyst.(3) A sweet-smelling compound formed by reacting acetic acid with ethanol in the presence of hydrochloric acid is ethyl acetate. OR(b) (i) Ethene is formed when ethanol at $443\,\mathrm{K}$ is heated with excess concentrated sulphuric acid.The mechanism of acid dehydration of ethanol to yield ethene is:1. First step is the protonation of oxygen atom of -OH group.2. Second step is the loss of a molecule of water to form carbonium ion.3. Last step is deprotonation to form carbon- carbon double bond. Concentrated sulphuric acid can act as a dehydrating agent. Hence, ethanol when heated at $433\,\mathrm{K}$ with excess conc. $\mathrm{H}_2\mathrm{SO}_4$ undergoes dehydration reaction to form ethene.(ii) Hydrogenation is the process of addition between hydrogen and other compounds in presence of a catalyst.For example: Alkene can be converted to alkane by using $\mathrm{H}_2$ in presence of metal catalyst such as $\mathrm{Pt},\ \mathrm{Ni}$ or $\mathrm{Pd}$ $\mathrm{CH_2=CH_2} \rightarrow \mathrm{CH_3CH_3}$ The industrial applications are as follows:1. To convert alkenes into alkanes.2. To prepare vegetable ghee from vegetable oils.