$$\eqalign{ & \mathop {{C_2}{H_5}OH}\limits_{\left( X \right)} + HI \to {C_2}{H_5}I + {H_2}O \cr & \mathop {C{H_3}OC{H_3}}\limits_{\left( Y \right)} + HI \to C{H_3}I + C{H_3}OH \cr} $$

$$cis$$  - cyclopenta - 1, 2 - diol when reacts with acetone, forms cyclic ketal whereas $$trans$$  - isomer of cyclopenta - 1, 2 - diol can not form cyclic ketal.

Among 20 naturally occuring amino acids "Cysteine" has  $$' - SH'$$  or thiol functional group.

$$ \Rightarrow {\text{Value of}}\,R = - C{H_2} - SH\,\,{\text{in Cysteine}}{\text{.}}$$

$$5KBr + KBr{O_3} + 3{H_2}O \to 3B{r_2} + 6KOH$$

The $$-OH$$  group of alcohol or the $$-COOH$$   group of a carboxylic acid is replaced by $$-Cl$$  using phosphorus penta chloride $$\left( {{\text{i}}{\text{.e}}{\text{.}}\,PC{l_5}} \right)$$
$$\eqalign{ & \mathop {ROH}\limits_{{\text{Alcohol}}} + PC{l_5} \to RCl + POC{l_3} + HCl \cr & \mathop {RCOOH}\limits_{{\text{Acid}}} + PC{l_5} \to RCOCl + POC{l_3} + HCl \cr} $$

No explanation is given for this question. Let's discuss the answer together.

Resonance stabilisation of phenoxide ion

\[{{C}_{2}}{{H}_{5}}-\underset{\text{Stable}}{\mathop{O}}\,-H\rightleftharpoons \underset{\begin{smallmatrix} \text{ Unstable} \\ \text{ ethoxide ion} \\ \text{(due to absence of resonance)} \end{smallmatrix}}{\mathop{{{C}_{2}}{{H}_{5}}-{{O}^{-}}+{{H}^{+}}}}\,\]
Phenoxide ion is more stable than ethoxide ion due to resonance. Therefore, the ionisation constant of phenol is higher than ethanol.

In dye test, phenolic $$ - OH$$  group is converted to $$ - {O^ - }$$  which activates the ring towards electrophilic aromatic substitution