(a) Increasing order of acidic strength:
p-nitrophenol in most acidic due to presence of −NO2 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 −CH3 group i.e., electron releasing group (+ I group) which destablises phenoxide ion so decreases acidity.
(b) Mechanism:
(i) Electrophilic attack of H3O+
H2O+H+‌(From acid) ‌→H3O+

(ii) Nucleophilic attack of water on carbocation.

(iii) Deprotonation:

OR
(a) When Butan-2-ol reacts with CrO3, it forms butan-2-one.
CH3−

CH |

OH

−CH2−CH3

CrO3

─────▸

CH3− C ∥ O −CH2−CH3

Butan−2−one

+H2O
(b) Butan-2-ol reacts with /SOCl2 to form 2-chlorobutane.
H−

H | C |

H

−

H | C |

OH

−

H | C |

H

−

H | C |

H

−H+SOCl2→

H− H | C | H − H | C | Cl − H | C | H − H | C | H −H

2−Chlorobutane

+SO2+HCl