(a) Increasing order of acidic strength: p-nitrophenol in most acidic due to presence of $- {NO}_2$ group i.e., electron with drawing group (-I group) which stabilises phenoxide ion so increases acidity while p-serve is least acidic due to presence of $- {CH}_ 3$ group i.e., electron releasing group (+ I group) which destablises phenoxide ion so decreases acidity. (b) Mechanism: (i) Electrophilic attack of ${H}_3 {O}^{+}$ ${H}_2 {O}+ {H}^{+} \;\text "(From acid) "\; \rightarrow{H}_3 {O}^{+}$ (ii) Nucleophilic attack of water on carbocation. (iii) Deprotonation: OR (a) When Butan-2-ol reacts with ${CrO}_3$, it forms butan-2-one. ${CH}_3- \underset{\mathrm{OH}}{\underset{\vert}{\mathrm{CH}}}- {CH}_2- {CH}_3 \overset{\mathrm{CrO}_3}{\rightarrow}$ ${ {CH}_3 - \underset{\mathrm{O}}{\underset{∥}{\mathrm{C}}}- {CH}_2- {CH}_3}↙{Butan-2-one}+ {H}_2 {O}$ (b) Butan-2-ol reacts with ${/SOCl}_2$ to form 2-chlorobutane. ${H}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\swarrow\underset{H}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\swarrow\underset{OH}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\swarrow\underset{H}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\swarrow\underset{H}{|}- {H}+ {SOCl}_2 \rightarrow$ ${{H}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\underset{H}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\underset{Cl}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\underset{H}{|}- \overset{\mathrm{H}}{\overset{\vert}{\mathrm{C}}}\underset{H}{|}- {H}}_{2-\text{Chlorobutane}}+ {SO}_2+ {HCl}$