Considering the reaction sequence given below, the correct statement(s) is(are)

The correct statements are:

1. Treating P with conc. NH₄OH solution followed by acidification gives Q.
2. Treating Q with a solution of NaNO₂ in aq. HCl liberates N₂.
3. P is more acidic than CH₃CH₂COOH.

Step-by-Step Analysis of the Reaction Sequence:

The given image shows the following reaction scheme:

1. Formation of Compound P:
Propanoic acid (${\text{CH}}_3{\text{CH}}_2\text{COOH}$) reacts with ${\text{Br}}_2$ in the presence of red phosphorus followed by hydrolysis (${\text{H}}_2\text{O}$). This is the Hell-Volhard-Zelinsky (HVZ) reaction, which causes α-bromination of carboxylic acids.

Thus, compound P is 2-bromopropanoic acid:

$\text{P}={\text{CH}}_3\text{CH(Br)COOH}$

2. Formation of Compound Q:
Compound P undergoes reaction with potassium phthalimide, followed by alkaline hydrolysis ($\text{NaOH}$) and acidification (${\text{H}}_3{\text{O}}^{+}$). This is the Gabriel Phthalimide Synthesis, which converts an alkyl halide into a primary amine without affecting the carboxylic group. Phthalic acid is formed as a side product.

Thus, compound Q is alanine (2-aminopropanoic acid):

$\text{Q}={\text{CH}}_3\text{CH(NH}{2}_{}\text{)COOH}$

Evaluation of the Given Statements:

Statement 1: "P can be reduced to a primary alcohol using NaBH₄."
${\text{NaBH}}_4$ is a weak reducing agent that reduces aldehydes and ketones but generally does not reduce carboxylic acid groups ($-\text{COOH}$) to alcohols. Therefore, P cannot be reduced to a primary alcohol using ${\text{NaBH}}_4$. Thus, this statement is incorrect.

Statement 2: "Treating P with conc. NH₄OH solution followed by acidification gives Q."
When 2-bromopropanoic acid (P) is treated with concentrated ammonia/ammonium hydroxide (${\text{NH}}_4\text{OH}$), nucleophilic substitution (${\text{S}}_{\text{N}}2$) occurs where the bromide ($-\text{Br}$) group is substituted by an amino ($-{\text{NH}}_2$) group, yielding 2-aminopropanoic acid (alanine, Q). Thus, this statement is correct.

Statement 3: "Treating Q with a solution of NaNO₂ in aq. HCl liberates N₂."
Compound Q is an aliphatic primary amine (an α-amino acid). Aliphatic primary amines react with nitrous acid (${\text{NaNO}}_2+\text{HCl}$) to form highly unstable aliphatic diazonium salts, which decompose immediately to release nitrogen gas (${\text{N}}_2$) quantitatively along with alcohols/hydroxy acids. Thus, this statement is correct.

Statement 4: "P is more acidic than CH₃CH₂COOH."
Compound P (2-bromopropanoic acid) contains an electronegative bromine atom at the α-position. Bromine exerts an electron-withdrawing inductive effect ($-\text{I}$ effect), which stabilizes the carboxylate anion formed after deprotonation. Consequently, P is significantly more acidic than unsubstituted propanoic acid (${\text{CH}}_3{\text{CH}}_2\text{COOH}$). Thus, this statement is correct.